--- a/gfx/layers/wr/WebRenderCommandBuilder.cpp
+++ b/gfx/layers/wr/WebRenderCommandBuilder.cpp
@@ -236,17 +236,16 @@ struct Grouper
 
 // Returns whether this is an item for which complete invalidation was
 // reliant on LayerTreeInvalidation in the pre-webrender world.
 static bool
 IsContainerLayerItem(nsDisplayItem* aItem)
 {
   switch (aItem->GetType()) {
     case DisplayItemType::TYPE_TRANSFORM:
-    case DisplayItemType::TYPE_LAYER_EVENT_REGIONS:
     case DisplayItemType::TYPE_OPACITY:
     case DisplayItemType::TYPE_FILTER:
     case DisplayItemType::TYPE_BLEND_CONTAINER:
     case DisplayItemType::TYPE_BLEND_MODE:
     case DisplayItemType::TYPE_MASK: {
       return true;
     }
     default: {
@@ -1232,20 +1231,16 @@ WebRenderCommandBuilder::CreateWebRender
 
   bool apzEnabled = mManager->AsyncPanZoomEnabled();
 
   FlattenedDisplayItemIterator iter(aDisplayListBuilder, aDisplayList);
   while (nsDisplayItem* i = iter.GetNext()) {
     nsDisplayItem* item = i;
     DisplayItemType itemType = item->GetType();
 
-    // We should never get event regions items in WR now that we always have
-    // WR hit-testing enabled.
-    MOZ_ASSERT(itemType != DisplayItemType::TYPE_LAYER_EVENT_REGIONS);
-
     // Peek ahead to the next item and try merging with it or swapping with it
     // if necessary.
     AutoTArray<nsDisplayItem*, 1> mergedItems;
     mergedItems.AppendElement(item);
     while (nsDisplayItem* peek = iter.PeekNext()) {
       if (!item->CanMerge(peek)) {
         break;
       }

--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -2829,26 +2829,21 @@ nsIFrame::BuildDisplayListForStackingCon
 
   const nsStyleDisplay* disp = StyleDisplay();
   const nsStyleEffects* effects = StyleEffects();
   EffectSet* effectSet = EffectSet::GetEffectSet(this);
   // We can stop right away if this is a zero-opacity stacking context and
   // we're painting, and we're not animating opacity. Don't do this
   // if we're going to compute plugin geometry, since opacity-0 plugins
   // need to have display items built for them.
-  bool needEventRegions =
-    aBuilder->IsBuildingLayerEventRegions() &&
-    StyleUserInterface()->GetEffectivePointerEvents(this) !=
-      NS_STYLE_POINTER_EVENTS_NONE;
   bool opacityItemForEventsAndPluginsOnly = false;
   if (effects->mOpacity == 0.0 && aBuilder->IsForPainting() &&
       !(disp->mWillChangeBitField & NS_STYLE_WILL_CHANGE_OPACITY) &&
       !nsLayoutUtils::HasAnimationOfProperty(effectSet, eCSSProperty_opacity)) {
-    if (needEventRegions ||
-        aBuilder->WillComputePluginGeometry()) {
+    if (aBuilder->WillComputePluginGeometry()) {
       opacityItemForEventsAndPluginsOnly = true;
     } else {
       return;
     }
   }
 
   if (disp->mWillChangeBitField != 0) {
     aBuilder->AddToWillChangeBudget(this, GetSize());
@@ -3077,23 +3072,16 @@ nsIFrame::BuildDisplayListForStackingCon
     if (extend3DContext) {
       // Mark these first so MarkAbsoluteFramesForDisplayList knows if we are
       // going to be forced to descend into frames.
       aBuilder->MarkPreserve3DFramesForDisplayList(this);
     }
 
     aBuilder->AdjustWindowDraggingRegion(this);
 
-    nsDisplayLayerEventRegions* eventRegions = nullptr;
-    if (aBuilder->IsBuildingLayerEventRegions()) {
-      eventRegions = MakeDisplayItem<nsDisplayLayerEventRegions>(aBuilder, this);
-      eventRegions->AddFrame(aBuilder, this);
-      aBuilder->SetLayerEventRegions(eventRegions);
-    }
-
     aBuilder->BuildCompositorHitTestInfoIfNeeded(this, set.BorderBackground(),
                                                  true);
 
     MarkAbsoluteFramesForDisplayList(aBuilder);
     aBuilder->Check();
     BuildDisplayList(aBuilder, set);
     aBuilder->Check();
 
@@ -3118,28 +3106,16 @@ nsIFrame::BuildDisplayListForStackingCon
     if (aBuilder->ContainsBlendMode() &&
         aBuilder->IsRetainingDisplayList()) {
       if (!aBuilder->GetDirtyRect().Contains(aBuilder->GetVisibleRect())) {
         aBuilder->SetPartialBuildFailed(true);
       } else {
         aBuilder->SetDisablePartialUpdates(true);
       }
     }
-
-    if (eventRegions) {
-      // If the event regions item ended up empty, throw it away rather than
-      // adding it to the display list.
-      if (!eventRegions->IsEmpty()) {
-        set.BorderBackground()->AppendToBottom(eventRegions);
-      } else {
-        aBuilder->SetLayerEventRegions(nullptr);
-        eventRegions->Destroy(aBuilder);
-        eventRegions = nullptr;
-      }
-    }
   }
 
   if (aBuilder->IsBackgroundOnly()) {
     set.BlockBorderBackgrounds()->DeleteAll(aBuilder);
     set.Floats()->DeleteAll(aBuilder);
     set.Content()->DeleteAll(aBuilder);
     set.PositionedDescendants()->DeleteAll(aBuilder);
     set.Outlines()->DeleteAll(aBuilder);
@@ -3543,18 +3519,17 @@ nsIFrame::BuildDisplayListForChild(nsDis
   nsIFrame* child = aChild;
   if (child->HasAnyStateBits(
        NS_FRAME_TOO_DEEP_IN_FRAME_TREE | NS_FRAME_IS_NONDISPLAY))
     return;
 
   aBuilder->ClearWillChangeBudget(child);
 
   const bool shortcutPossible = aBuilder->IsPaintingToWindow() &&
-    (aBuilder->IsBuildingLayerEventRegions() ||
-     aBuilder->BuildCompositorHitTestInfo());
+     aBuilder->BuildCompositorHitTestInfo();
 
   const bool doingShortcut = shortcutPossible &&
     (child->GetStateBits() & NS_FRAME_SIMPLE_DISPLAYLIST) &&
     // Animations may change the value of |HasOpacity()|.
     !(child->GetContent() &&
       child->GetContent()->MayHaveAnimations());
 
   // dirty rect in child-relative coordinates
@@ -3579,21 +3554,16 @@ nsIFrame::BuildDisplayListForChild(nsDis
       buildingForChild(aBuilder, child, visible, dirty, false);
 
     CheckForApzAwareEventHandlers(aBuilder, child);
 
     aBuilder->BuildCompositorHitTestInfoIfNeeded(child,
                                                  aLists.BorderBackground(),
                                                  false);
 
-    nsDisplayLayerEventRegions* eventRegions = aBuilder->GetLayerEventRegions();
-    if (eventRegions) {
-      eventRegions->AddFrame(aBuilder, child);
-    }
-
     child->MarkAbsoluteFramesForDisplayList(aBuilder);
     aBuilder->AdjustWindowDraggingRegion(child);
     aBuilder->Check();
     child->BuildDisplayList(aBuilder, aLists);
     aBuilder->Check();
     aBuilder->DisplayCaret(child, aLists.Content());
 #ifdef DEBUG
     DisplayDebugBorders(aBuilder, child, aLists);
@@ -3793,40 +3763,16 @@ nsIFrame::BuildDisplayListForChild(nsDis
       aBuilder->IntersectDirtyRect(*clipPropClip);
       clipState.ClipContentDescendants(
         *clipPropClip + aBuilder->ToReferenceFrame(child));
       awayFromCommonPath = true;
     }
 
     child->MarkAbsoluteFramesForDisplayList(aBuilder);
 
-    if (aBuilder->IsBuildingLayerEventRegions()) {
-      // If this frame has a different animated geometry root than its parent,
-      // make sure we accumulate event regions for its layer.
-      if (buildingForChild.IsAnimatedGeometryRoot() || isPositioned) {
-        nsDisplayLayerEventRegions* eventRegions =
-          MakeDisplayItem<nsDisplayLayerEventRegions>(aBuilder, child);
-        eventRegions->AddFrame(aBuilder, child);
-        aBuilder->SetLayerEventRegions(eventRegions);
-
-        if (isPositioned) {
-          // We need this nsDisplayLayerEventRegions to be sorted with the positioned
-          // elements as positioned elements will be sorted on top of normal elements
-          list.AppendToTop(eventRegions);
-        } else {
-          aLists.BorderBackground()->AppendToTop(eventRegions);
-        }
-      } else {
-        nsDisplayLayerEventRegions* eventRegions = aBuilder->GetLayerEventRegions();
-        if (eventRegions) {
-          eventRegions->AddFrame(aBuilder, child);
-        }
-      }
-    }
-
     const bool differentAGR =
       buildingForChild.IsAnimatedGeometryRoot() || isPositioned;
 
     if (!awayFromCommonPath && shortcutPossible &&
         !differentAGR && !buildingForChild.MaybeAnimatedGeometryRoot()) {
       // The shortcut is available for the child for next time.
       child->AddStateBits(NS_FRAME_SIMPLE_DISPLAYLIST);
     }

--- a/layout/generic/nsGfxScrollFrame.cpp
+++ b/layout/generic/nsGfxScrollFrame.cpp
@@ -3691,22 +3691,16 @@ ScrollFrameHelper::BuildDisplayList(nsDi
             scrollbarStyles.mOverscrollBehaviorY != StyleOverscrollBehavior::Auto) {
           info |= CompositorHitTestInfo::eRequiresTargetConfirmation;
         }
         nsDisplayCompositorHitTestInfo* hitInfo =
             MakeDisplayItem<nsDisplayCompositorHitTestInfo>(aBuilder, mScrolledFrame, info, 1,
                 Some(mScrollPort + aBuilder->ToReferenceFrame(mOuter)));
         AppendInternalItemToTop(scrolledContent, hitInfo, Some(INT32_MAX));
       }
-      if (aBuilder->IsBuildingLayerEventRegions()) {
-        nsDisplayLayerEventRegions* inactiveRegionItem =
-            MakeDisplayItem<nsDisplayLayerEventRegions>(aBuilder, mScrolledFrame, 1);
-        inactiveRegionItem->AddInactiveScrollPort(mScrolledFrame, mScrollPort + aBuilder->ToReferenceFrame(mOuter));
-        AppendInternalItemToTop(scrolledContent, inactiveRegionItem, Some(INT32_MAX));
-      }
     }
 
     if (aBuilder->ShouldBuildScrollInfoItemsForHoisting()) {
       aBuilder->AppendNewScrollInfoItemForHoisting(
         MakeDisplayItem<nsDisplayScrollInfoLayer>(aBuilder, mScrolledFrame,
                                                 mOuter));
     }
   }

--- a/layout/painting/FrameLayerBuilder.cpp
+++ b/layout/painting/FrameLayerBuilder.cpp
@@ -583,24 +583,17 @@ public:
   AnimatedGeometryRoot* GetAnimatedGeometryRoot() { return mAnimatedGeometryRoot; }
 
   /**
    * A region including the horizontal pan, vertical pan, and no action regions.
    */
   nsRegion CombinedTouchActionRegion();
 
   /**
-   * Add the given hit regions to the hit regions for this PaintedLayer.
-   */
-  void AccumulateEventRegions(ContainerState* aState,
-                              nsDisplayLayerEventRegions* aEventRegions);
-
-  /**
-   * Similar to AccumulateEventRegions() but uses different display item to
-   * track hit regions.
+   * Add the given hit test info to the hit regions for this PaintedLayer.
    */
   void AccumulateHitTestInfo(ContainerState* aState,
                              nsDisplayCompositorHitTestInfo* aItem);
 
   /**
    * If this represents only a nsDisplayImage, and the image type supports being
    * optimized to an ImageLayer, returns true.
    */
@@ -3399,17 +3392,16 @@ void ContainerState::FinishPaintedLayerD
   if (!layer) {
     // We couldn't optimize to an image layer or a color layer above.
     layer = data->mLayer;
     layer->SetClipRect(Nothing());
     FLB_LOG_PAINTED_LAYER_DECISION(data, "  Selected painted layer=%p\n", layer.get());
   }
 
   for (auto& item : data->mAssignedDisplayItems) {
-    MOZ_ASSERT(item.mItem->GetType() != DisplayItemType::TYPE_LAYER_EVENT_REGIONS);
     MOZ_ASSERT(item.mItem->GetType() != DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO);
 
     if (item.mType == DisplayItemEntryType::POP_OPACITY) {
       // Do not invalidate for end markers.
       continue;
     }
 
     InvalidateForLayerChange(item.mItem, data->mLayer, item.mDisplayItemData);
@@ -3819,48 +3811,16 @@ PaintedLayerData::CombinedTouchActionReg
 {
   nsRegion result;
   result.Or(mHorizontalPanRegion, mVerticalPanRegion);
   result.OrWith(mNoActionRegion);
   return result;
 }
 
 void
-PaintedLayerData::AccumulateEventRegions(ContainerState* aState, nsDisplayLayerEventRegions* aEventRegions)
-{
-  FLB_LOG_PAINTED_LAYER_DECISION(this, "Accumulating event regions %p against pld=%p\n", aEventRegions, this);
-
-  mHitRegion.OrWith(aEventRegions->HitRegion());
-  mMaybeHitRegion.OrWith(aEventRegions->MaybeHitRegion());
-  mDispatchToContentHitRegion.OrWith(aEventRegions->DispatchToContentHitRegion());
-
-  // See the comment in nsDisplayList::AddFrame, where the touch action regions
-  // are handled. The same thing applies here.
-  bool alreadyHadRegions = !mNoActionRegion.IsEmpty() ||
-      !mHorizontalPanRegion.IsEmpty() ||
-      !mVerticalPanRegion.IsEmpty();
-  mNoActionRegion.OrWith(aEventRegions->NoActionRegion());
-  mHorizontalPanRegion.OrWith(aEventRegions->HorizontalPanRegion());
-  mVerticalPanRegion.OrWith(aEventRegions->VerticalPanRegion());
-  if (alreadyHadRegions) {
-    mDispatchToContentHitRegion.OrWith(CombinedTouchActionRegion());
-  }
-
-  // Avoid quadratic performance as a result of the region growing to include
-  // and arbitrarily large number of rects, which can happen on some pages.
-  mMaybeHitRegion.SimplifyOutward(8);
-  mDispatchToContentHitRegion.SimplifyOutward(8);
-
-  // Calculate scaled versions of the bounds of mHitRegion and mMaybeHitRegion
-  // for quick access in FindPaintedLayerFor().
-  mScaledHitRegionBounds = aState->ScaleToOutsidePixels(mHitRegion.GetBounds());
-  mScaledMaybeHitRegionBounds = aState->ScaleToOutsidePixels(mMaybeHitRegion.GetBounds());
-}
-
-void
 PaintedLayerData::AccumulateHitTestInfo(ContainerState* aState,
                                         nsDisplayCompositorHitTestInfo* aItem)
 {
   FLB_LOG_PAINTED_LAYER_DECISION(this,
     "Accumulating hit test info %p against pld=%p\n", aItem, this);
 
   const mozilla::DisplayItemClip& clip = aItem->GetClip();
   const nsRect area = clip.ApplyNonRoundedIntersection(aItem->Area());
@@ -4292,21 +4252,16 @@ ContainerState::ProcessDisplayItems(nsDi
 {
   AUTO_PROFILER_LABEL("ContainerState::ProcessDisplayItems", GRAPHICS);
 
   nsPoint topLeft(0,0);
 
   int32_t maxLayers = gfxPrefs::MaxActiveLayers();
   int layerCount = 0;
 
-#ifdef DEBUG
-  bool hadLayerEventRegions = false;
-  bool hadCompositorHitTestInfo = false;
-#endif
-
   if (!mManager->IsWidgetLayerManager()) {
     mPaintedLayerDataTree.InitializeForInactiveLayer(mContainerAnimatedGeometryRoot);
   }
 
   AnimatedGeometryRoot* lastAnimatedGeometryRoot = nullptr;
   nsPoint lastTopLeft;
 
   // Tracks the PaintedLayerData that the item will be accumulated in, if it is
@@ -4319,45 +4274,25 @@ ContainerState::ProcessDisplayItems(nsDi
     nsDisplayItem* i = e.mItem;
     DisplayItemEntryType marker = e.mType;
 
 
     nsDisplayItem* item = i;
     MOZ_ASSERT(item);
     DisplayItemType itemType = item->GetType();
 
-    // If the item is a event regions item, but is empty (has no regions in it)
-    // then we should just throw it out
-    if (itemType == DisplayItemType::TYPE_LAYER_EVENT_REGIONS) {
-#ifdef DEBUG
-      hadLayerEventRegions = true;
-#endif
-      nsDisplayLayerEventRegions* eventRegions =
-        static_cast<nsDisplayLayerEventRegions*>(item);
-
-      if (eventRegions->IsEmpty()) {
-        continue;
-      }
-    }
-
     if (itemType == DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO) {
-#ifdef DEBUG
-      hadCompositorHitTestInfo = true;
-#endif
       nsDisplayCompositorHitTestInfo* hitTestInfo =
         static_cast<nsDisplayCompositorHitTestInfo*>(item);
 
       if (hitTestInfo->Area().IsEmpty()) {
         continue;
       }
     }
 
-    // Only allow either LayerEventRegions or CompositorHitTestInfo items.
-    MOZ_ASSERT(!(hadLayerEventRegions && hadCompositorHitTestInfo));
-
     if (marker == DisplayItemEntryType::ITEM) {
       // Peek ahead to the next item and see if it can be merged with the
       // current item.
       nsDisplayItem* peek = iter.PeekNext();
       if (peek && item->CanMerge(peek)) {
         // Create a list of consecutive items that can be merged together.
         AutoTArray<nsDisplayItem*, 2> mergedItems { item };
         while ((peek = iter.PeekNext())) {
@@ -4384,18 +4319,17 @@ ContainerState::ProcessDisplayItems(nsDi
     NS_ASSERTION(mAppUnitsPerDevPixel == AppUnitsPerDevPixel(item),
       "items in a container layer should all have the same app units per dev pixel");
 
     if (mBuilder->NeedToForceTransparentSurfaceForItem(item)) {
       aList->SetNeedsTransparentSurface();
     }
 
     if (mParameters.mForEventsAndPluginsOnly && !item->GetChildren() &&
-        (itemType != DisplayItemType::TYPE_LAYER_EVENT_REGIONS &&
-         itemType != DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO &&
+        (itemType != DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO &&
          itemType != DisplayItemType::TYPE_PLUGIN)) {
       continue;
     }
 
     LayerState layerState = LAYER_NONE;
 
     if (marker == DisplayItemEntryType::ITEM) {
       layerState = item->GetLayerState(mBuilder, mManager, mParameters);
@@ -4435,26 +4369,21 @@ ContainerState::ProcessDisplayItems(nsDi
       lastAnimatedGeometryRoot = animatedGeometryRoot;
     }
 
     const ActiveScrolledRoot* scrollMetadataASR =
         layerClipChain ? ActiveScrolledRoot::PickDescendant(itemASR, layerClipChain->mASR) : itemASR;
 
     bool snap;
     nsRect itemContent = item->GetBounds(mBuilder, &snap);
-    if (itemType == DisplayItemType::TYPE_LAYER_EVENT_REGIONS) {
-      nsDisplayLayerEventRegions* eventRegions =
-        static_cast<nsDisplayLayerEventRegions*>(item);
-      itemContent = eventRegions->GetHitRegionBounds(mBuilder, &snap);
-    }
 
     if (itemType == DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO) {
-      nsDisplayCompositorHitTestInfo* eventRegions =
+      nsDisplayCompositorHitTestInfo* hitInfo =
         static_cast<nsDisplayCompositorHitTestInfo*>(item);
-      itemContent = eventRegions->Area();
+      itemContent = hitInfo->Area();
     }
 
     nsIntRect itemDrawRect = ScaleToOutsidePixels(itemContent, snap);
     bool prerenderedTransform = itemType == DisplayItemType::TYPE_TRANSFORM &&
         static_cast<nsDisplayTransform*>(item)->MayBeAnimated(mBuilder);
     ParentLayerIntRect clipRect;
     const DisplayItemClip& itemClip = item->GetClip();
     if (itemClip.HasClip()) {
@@ -4463,18 +4392,17 @@ ContainerState::ProcessDisplayItems(nsDi
       if (!prerenderedTransform && !IsScrollThumbLayer(item)) {
         itemDrawRect.IntersectRect(itemDrawRect, clipRect.ToUnknownRect());
       }
       clipRect.MoveBy(ViewAs<ParentLayerPixel>(mParameters.mOffset));
     }
 #ifdef DEBUG
     nsRect bounds = itemContent;
 
-    if (itemType == DisplayItemType::TYPE_LAYER_EVENT_REGIONS ||
-        itemType == DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO) {
+    if (itemType == DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO) {
       bounds.SetEmpty();
     }
 
     if (!bounds.IsEmpty()) {
       if (itemASR != mContainerASR) {
         if (Maybe<nsRect> clip = item->GetClipWithRespectToASR(mBuilder, mContainerASR)) {
           bounds = clip.ref();
         }
@@ -4839,21 +4767,17 @@ ContainerState::ProcessDisplayItems(nsDi
                                                     [&](PaintedLayerData* aData) {
             NewPaintedLayerData(aData, animatedGeometryRoot, itemASR,
                                 layerClipChain, scrollMetadataASR, topLeft,
                                 referenceFrame, backfaceHidden);
         });
       }
       MOZ_ASSERT(paintedLayerData);
 
-      if (itemType == DisplayItemType::TYPE_LAYER_EVENT_REGIONS) {
-        nsDisplayLayerEventRegions* eventRegions =
-          static_cast<nsDisplayLayerEventRegions*>(item);
-        paintedLayerData->AccumulateEventRegions(this, eventRegions);
-      } else if (itemType == DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO) {
+      if (itemType == DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO) {
         nsDisplayCompositorHitTestInfo* hitTestInfo =
           static_cast<nsDisplayCompositorHitTestInfo*>(item);
         paintedLayerData->AccumulateHitTestInfo(this, hitTestInfo);
       } else {
         paintedLayerData->Accumulate(this, item, itemVisibleRect, itemContent, itemClip,
                                      layerState, aList, marker);
 
         if (!paintedLayerData->mLayer) {

--- a/layout/painting/nsDisplayItemTypesList.h
+++ b/layout/painting/nsDisplayItemTypesList.h
@@ -27,17 +27,16 @@ DECLARE_DISPLAY_ITEM_TYPE(CANVAS_FOCUS, 
 DECLARE_DISPLAY_ITEM_TYPE(CARET, TYPE_RENDERS_NO_IMAGES)
 DECLARE_DISPLAY_ITEM_TYPE(CHECKED_CHECKBOX, TYPE_RENDERS_NO_IMAGES)
 DECLARE_DISPLAY_ITEM_TYPE(CHECKED_RADIOBUTTON, TYPE_RENDERS_NO_IMAGES)
 DECLARE_DISPLAY_ITEM_TYPE(CLEAR_BACKGROUND, TYPE_RENDERS_NO_IMAGES)
 DECLARE_DISPLAY_ITEM_TYPE(COLUMN_RULE, TYPE_RENDERS_NO_IMAGES)
 DECLARE_DISPLAY_ITEM_TYPE(COMBOBOX_FOCUS, TYPE_RENDERS_NO_IMAGES)
 DECLARE_DISPLAY_ITEM_TYPE(COMPOSITOR_HITTEST_INFO, TYPE_RENDERS_NO_IMAGES)
 DECLARE_DISPLAY_ITEM_TYPE(EVENT_RECEIVER, TYPE_RENDERS_NO_IMAGES)
-DECLARE_DISPLAY_ITEM_TYPE(LAYER_EVENT_REGIONS, TYPE_RENDERS_NO_IMAGES)
 DECLARE_DISPLAY_ITEM_TYPE(FIELDSET_BORDER_BACKGROUND, 0)
 DECLARE_DISPLAY_ITEM_TYPE(FIXED_POSITION, TYPE_RENDERS_NO_IMAGES)
 DECLARE_DISPLAY_ITEM_TYPE(STICKY_POSITION, TYPE_RENDERS_NO_IMAGES)
 DECLARE_DISPLAY_ITEM_TYPE(FRAMESET_BORDER, TYPE_RENDERS_NO_IMAGES)
 DECLARE_DISPLAY_ITEM_TYPE(FRAMESET_BLANK, TYPE_RENDERS_NO_IMAGES)
 DECLARE_DISPLAY_ITEM_TYPE(HEADER_FOOTER, TYPE_RENDERS_NO_IMAGES)
 DECLARE_DISPLAY_ITEM_TYPE(IMAGE, 0)
 DECLARE_DISPLAY_ITEM_TYPE(LIST_FOCUS, TYPE_RENDERS_NO_IMAGES)

--- a/layout/painting/nsDisplayList.cpp
+++ b/layout/painting/nsDisplayList.cpp
@@ -976,17 +976,16 @@ nsDisplayListBuilder::AutoCurrentActiveS
 
   mUsed = true;
 }
 
 nsDisplayListBuilder::nsDisplayListBuilder(nsIFrame* aReferenceFrame,
     nsDisplayListBuilderMode aMode, bool aBuildCaret, bool aRetainingDisplayList)
     : mReferenceFrame(aReferenceFrame),
       mIgnoreScrollFrame(nullptr),
-      mLayerEventRegions(nullptr),
       mCompositorHitTestInfo(nullptr),
       mCurrentTableItem(nullptr),
       mCurrentActiveScrolledRoot(nullptr),
       mCurrentContainerASR(nullptr),
       mCurrentFrame(aReferenceFrame),
       mCurrentReferenceFrame(aReferenceFrame),
       mRootAGR(AnimatedGeometryRoot::CreateAGRForFrame(aReferenceFrame, nullptr, true, aRetainingDisplayList)),
       mCurrentAGR(mRootAGR),
@@ -1071,17 +1070,16 @@ nsDisplayListBuilder::EndFrame()
 {
   NS_ASSERTION(!mInInvalidSubtree, "Someone forgot to cleanup mInInvalidSubtree!");
   mFrameToAnimatedGeometryRootMap.Clear();
   mActiveScrolledRoots.Clear();
   FreeClipChains();
   FreeTemporaryItems();
   nsCSSRendering::EndFrameTreesLocked();
 
-  MOZ_ASSERT(!mLayerEventRegions);
   MOZ_ASSERT(!mCompositorHitTestInfo);
 }
 
 void
 nsDisplayListBuilder::MarkFrameForDisplay(nsIFrame* aFrame, nsIFrame* aStopAtFrame)
 {
   mFramesMarkedForDisplay.AppendElement(aFrame);
   for (nsIFrame* f = aFrame; f;
@@ -1370,17 +1368,16 @@ nsDisplayListBuilder::EnterPresShell(nsI
 }
 
 // A non-blank paint is a paint that does not just contain the canvas background.
 static bool
 DisplayListIsNonBlank(nsDisplayList* aList)
 {
   for (nsDisplayItem* i = aList->GetBottom(); i != nullptr; i = i->GetAbove()) {
     switch (i->GetType()) {
-      case DisplayItemType::TYPE_LAYER_EVENT_REGIONS:
       case DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO:
       case DisplayItemType::TYPE_CANVAS_BACKGROUND_COLOR:
       case DisplayItemType::TYPE_CANVAS_BACKGROUND_IMAGE:
         continue;
       case DisplayItemType::TYPE_SOLID_COLOR:
       case DisplayItemType::TYPE_BACKGROUND:
       case DisplayItemType::TYPE_BACKGROUND_COLOR:
         if (i->Frame()->IsCanvasFrame()) {
@@ -2286,31 +2283,16 @@ nsDisplayListBuilder::ShouldBuildComposi
     // Hit test flags are different.
     return true;
   }
 
   // Create a new item if the parent does not contain the child completely.
   return !mCompositorHitTestInfo->Area().Contains(GetFrameArea(this, aFrame));
 }
 
-bool
-nsDisplayListBuilder::IsBuildingLayerEventRegions()
-{
-  if (mBuildCompositorHitTestInfo) {
-    // If we have webrender hit-testing enabled, then we will build the
-    // nsDisplayCompositorHitTestInfo items and use those instead of event
-    // regions, so we don't need to build the event regions.
-    return false;
-  }
-  if (IsPaintingToWindow()) {
-    return mAsyncPanZoomEnabled;
-  }
-  return false;
-}
-
 void nsDisplayListSet::MoveTo(const nsDisplayListSet& aDestination) const
 {
   aDestination.BorderBackground()->AppendToTop(BorderBackground());
   aDestination.BlockBorderBackgrounds()->AppendToTop(BlockBorderBackgrounds());
   aDestination.Floats()->AppendToTop(Floats());
   aDestination.Content()->AppendToTop(Content());
   aDestination.PositionedDescendants()->AppendToTop(PositionedDescendants());
   aDestination.Outlines()->AppendToTop(Outlines());
@@ -2377,17 +2359,16 @@ nsDisplayList::ComputeVisibilityForRoot(
 }
 
 static nsRegion
 TreatAsOpaque(nsDisplayItem* aItem, nsDisplayListBuilder* aBuilder)
 {
   bool snap;
   nsRegion opaque = aItem->GetOpaqueRegion(aBuilder, &snap);
   if (aBuilder->IsForPluginGeometry() &&
-      aItem->GetType() != DisplayItemType::TYPE_LAYER_EVENT_REGIONS &&
       aItem->GetType() != DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO)
   {
     // Treat all leaf chrome items as opaque, unless their frames are opacity:0.
     // Since opacity:0 frames generate an nsDisplayOpacity, that item will
     // not be treated as opaque here, so opacity:0 chrome content will be
     // effectively ignored, as it should be.
     // We treat leaf chrome items as opaque to ensure that they cover
     // content plugins, for security reasons.
@@ -5134,213 +5115,16 @@ nsDisplayCompositorHitTestInfo::ZIndex()
 }
 
 void
 nsDisplayCompositorHitTestInfo::SetOverrideZIndex(int32_t aZIndex)
 {
   mOverrideZIndex = Some(aZIndex);
 }
 
-void
-nsDisplayLayerEventRegions::AddFrame(nsDisplayListBuilder* aBuilder,
-                                     nsIFrame* aFrame)
-{
-  NS_ASSERTION(aBuilder->FindReferenceFrameFor(aFrame) == aBuilder->FindReferenceFrameFor(mFrame),
-               "Reference frame mismatch");
-  CompositorHitTestInfo hitInfo =
-      aFrame->GetCompositorHitTestInfo(aBuilder);
-  if (hitInfo == CompositorHitTestInfo::eInvisibleToHitTest) {
-    return;
-  }
-
-  // XXX handle other pointerEvents values for SVG
-
-  // XXX Do something clever here for the common case where the border box
-  // is obviously entirely inside mHitRegion.
-  nsRect borderBox = GetFrameArea(aBuilder, aFrame);
-
-  if (aFrame != mFrame &&
-      aBuilder->IsRetainingDisplayList()) {
-    aFrame->AddDisplayItem(this);
-  }
-
-  bool borderBoxHasRoundedCorners = false;
-
-  // use the NS_FRAME_SIMPLE_EVENT_REGIONS to avoid calling the slightly
-  // expensive HasNonZeroCorner function if we know from a previous run that
-  // the frame has zero corners.
-  bool simpleRegions = aFrame->HasAnyStateBits(NS_FRAME_SIMPLE_EVENT_REGIONS);
-  if (!simpleRegions) {
-    if (nsLayoutUtils::HasNonZeroCorner(aFrame->StyleBorder()->mBorderRadius)) {
-      borderBoxHasRoundedCorners = true;
-    } else {
-      aFrame->AddStateBits(NS_FRAME_SIMPLE_EVENT_REGIONS);
-    }
-  }
-
-  const DisplayItemClip* clip = DisplayItemClipChain::ClipForASR(
-    aBuilder->ClipState().GetCurrentCombinedClipChain(aBuilder),
-    aBuilder->CurrentActiveScrolledRoot());
-  if (clip) {
-    borderBox = clip->ApplyNonRoundedIntersection(borderBox);
-    if (clip->GetRoundedRectCount() > 0) {
-      borderBoxHasRoundedCorners = true;
-    }
-  }
-
-  if (borderBoxHasRoundedCorners ||
-      (aFrame->GetStateBits() & NS_FRAME_SVG_LAYOUT)) {
-    mMaybeHitRegion.Add(aFrame, borderBox);
-  } else {
-    mHitRegion.Add(aFrame, borderBox);
-  }
-
-  if (hitInfo & CompositorHitTestInfo::eDispatchToContent) {
-    mDispatchToContentHitRegion.Add(aFrame, borderBox);
-  }
-
-  // Touch action region
-
-  auto touchFlags = hitInfo & CompositorHitTestInfo::eTouchActionMask;
-  if (touchFlags) {
-    // something was disabled
-    if (touchFlags == CompositorHitTestInfo::eTouchActionMask) {
-      // everything was disabled, so touch-action:none
-      mNoActionRegion.Add(aFrame, borderBox);
-    } else {
-      // The event regions code does not store enough information to actually
-      // represent all the different states. Prior to the introduction of
-      // CompositorHitTestInfo here in bug 1389149, the following two cases
-      // were effectively getting collapsed:
-      //   (1) touch-action: auto
-      //   (2) touch-action: manipulation
-      // In both of these cases, none of {mNoActionRegion, mHorizontalPanRegion,
-      // mVerticalPanRegion} were modified, and so the fact that case (2) should
-      // have prevented double-tap-zooming was getting lost.
-      // With CompositorHitTestInfo we can now represent that case correctly,
-      // but only if we use CompositorHitTestInfo all the way to the compositor
-      // (i.e. in the WebRender-enabled case). In the non-WebRender case where
-      // we still use the event regions, we must collapse these two cases back
-      // together. Or add another region to the event regions to fix this
-      // properly.
-      if (touchFlags == CompositorHitTestInfo::eTouchActionDoubleTapZoomDisabled) {
-        // the touch-action: manipulation case described above. To preserve the
-        // existing behaviour, don't touch either mHorizontalPanRegion or
-        // mVerticalPanRegion
-      } else {
-        if (!(hitInfo & CompositorHitTestInfo::eTouchActionPanXDisabled)) {
-          // pan-x is allowed
-          mHorizontalPanRegion.Add(aFrame, borderBox);
-        }
-        if (!(hitInfo & CompositorHitTestInfo::eTouchActionPanYDisabled)) {
-          // pan-y is allowed
-          mVerticalPanRegion.Add(aFrame, borderBox);
-        }
-      }
-    }
-  }
-}
-
-static void
-RemoveFrameFromFrameRects(nsDisplayLayerEventRegions::FrameRects& aFrameRects, nsIFrame* aFrame)
-{
-  uint32_t i = 0;
-  uint32_t length = aFrameRects.mFrames.Length();
-  while (i < length) {
-    if (aFrameRects.mFrames[i] == aFrame) {
-      aFrameRects.mFrames[i] = aFrameRects.mFrames[length - 1];
-      aFrameRects.mBoxes[i] = aFrameRects.mBoxes[length - 1];
-      length--;
-    } else {
-      i++;
-    }
-  }
-  aFrameRects.mFrames.SetLength(length);
-  aFrameRects.mBoxes.SetLength(length);
-}
-
-void
-nsDisplayLayerEventRegions::RemoveFrame(nsIFrame* aFrame)
-{
-  RemoveFrameFromFrameRects(mHitRegion, aFrame);
-  RemoveFrameFromFrameRects(mMaybeHitRegion, aFrame);
-  RemoveFrameFromFrameRects(mDispatchToContentHitRegion, aFrame);
-  RemoveFrameFromFrameRects(mNoActionRegion, aFrame);
-  RemoveFrameFromFrameRects(mHorizontalPanRegion, aFrame);
-  RemoveFrameFromFrameRects(mVerticalPanRegion, aFrame);
-
-  nsDisplayItem::RemoveFrame(aFrame);
-}
-
-void
-nsDisplayLayerEventRegions::AddInactiveScrollPort(nsIFrame* aFrame, const nsRect& aRect)
-{
-  mHitRegion.Add(aFrame, aRect);
-  mDispatchToContentHitRegion.Add(aFrame, aRect);
-}
-
-bool
-nsDisplayLayerEventRegions::IsEmpty() const
-{
-  // If the hit region and maybe-hit region are empty, then the rest
-  // must be empty too.
-  if (mHitRegion.IsEmpty() && mMaybeHitRegion.IsEmpty()) {
-    MOZ_ASSERT(mDispatchToContentHitRegion.IsEmpty());
-    MOZ_ASSERT(mNoActionRegion.IsEmpty());
-    MOZ_ASSERT(mHorizontalPanRegion.IsEmpty());
-    MOZ_ASSERT(mVerticalPanRegion.IsEmpty());
-    return true;
-  }
-  return false;
-}
-
-nsRegion
-nsDisplayLayerEventRegions::CombinedTouchActionRegion()
-{
-  nsRegion result;
-  result.Or(HorizontalPanRegion(), VerticalPanRegion());
-  result.OrWith(NoActionRegion());
-  return result;
-}
-
-int32_t
-nsDisplayLayerEventRegions::ZIndex() const
-{
-  return mOverrideZIndex ? *mOverrideZIndex : nsDisplayItem::ZIndex();
-}
-
-void
-nsDisplayLayerEventRegions::SetOverrideZIndex(int32_t aZIndex)
-{
-  mOverrideZIndex = Some(aZIndex);
-}
-
-void
-nsDisplayLayerEventRegions::WriteDebugInfo(std::stringstream& aStream)
-{
-  if (!mHitRegion.IsEmpty()) {
-    AppendToString(aStream, HitRegion(), " (hitRegion ", ")");
-  }
-  if (!mMaybeHitRegion.IsEmpty()) {
-    AppendToString(aStream, MaybeHitRegion(), " (maybeHitRegion ", ")");
-  }
-  if (!mDispatchToContentHitRegion.IsEmpty()) {
-    AppendToString(aStream, DispatchToContentHitRegion(), " (dispatchToContentRegion ", ")");
-  }
-  if (!mNoActionRegion.IsEmpty()) {
-    AppendToString(aStream, NoActionRegion(), " (noActionRegion ", ")");
-  }
-  if (!mHorizontalPanRegion.IsEmpty()) {
-    AppendToString(aStream, HorizontalPanRegion(), " (horizPanRegion ", ")");
-  }
-  if (!mVerticalPanRegion.IsEmpty()) {
-    AppendToString(aStream, VerticalPanRegion(), " (vertPanRegion ", ")");
-  }
-}
-
 nsDisplayCaret::nsDisplayCaret(nsDisplayListBuilder* aBuilder,
                                nsIFrame* aCaretFrame)
   : nsDisplayItem(aBuilder, aCaretFrame)
   , mCaret(aBuilder->GetCaret())
   , mBounds(aBuilder->GetCaretRect() + ToReferenceFrame())
 {
   MOZ_COUNT_CTOR(nsDisplayCaret);
 }
@@ -6574,18 +6358,17 @@ CollectItemsWithOpacity(nsDisplayList* a
     // Descend only into wraplists.
     if (type == DisplayItemType::TYPE_WRAP_LIST && children) {
       // The current display item has children, process them first.
       if (!CollectItemsWithOpacity(children, aArray, aMaxChildCount)) {
         return false;
       }
     }
 
-    if (type == DisplayItemType::TYPE_LAYER_EVENT_REGIONS ||
-        type == DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO ||
+    if (type == DisplayItemType::TYPE_COMPOSITOR_HITTEST_INFO ||
         type == DisplayItemType::TYPE_WRAP_LIST) {
       continue;
     }
 
     if (!i->CanApplyOpacity() || aArray.Length() == aMaxChildCount) {
       return false;
     }
 

--- a/layout/painting/nsDisplayList.h
+++ b/layout/painting/nsDisplayList.h
@@ -57,17 +57,16 @@
 
 class gfxContext;
 class nsIContent;
 class nsDisplayList;
 class nsDisplayTableItem;
 class nsIScrollableFrame;
 class nsSubDocumentFrame;
 class nsDisplayCompositorHitTestInfo;
-class nsDisplayLayerEventRegions;
 class nsDisplayScrollInfoLayer;
 class nsCaret;
 enum class nsDisplayOwnLayerFlags;
 
 namespace mozilla {
 class FrameLayerBuilder;
 namespace layers {
 class Layer;
@@ -721,22 +720,16 @@ public:
 
   /**
    * Returns true if merging and flattening of display lists should be
    * performed while computing visibility.
    */
   bool AllowMergingAndFlattening() { return mAllowMergingAndFlattening; }
   void SetAllowMergingAndFlattening(bool aAllow) { mAllowMergingAndFlattening = aAllow; }
 
-  nsDisplayLayerEventRegions* GetLayerEventRegions() { return mLayerEventRegions; }
-  void SetLayerEventRegions(nsDisplayLayerEventRegions* aItem)
-  {
-    mLayerEventRegions = aItem;
-  }
-
   /**
    * Sets the current compositor hit test info to |aHitTestInfo|.
    * This is used during display list building to determine if the parent frame
    * hit test info contains the same information that child frame needs.
    */
   void SetCompositorHitTestInfo(nsDisplayCompositorHitTestInfo* aHitTestInfo)
   {
     mCompositorHitTestInfo = aHitTestInfo;
@@ -750,17 +743,16 @@ public:
    * Builds a new nsDisplayCompositorHitTestInfo for the frame |aFrame| if
    * needed, and adds it to the top of |aList|. If |aBuildNew| is true, the
    * previous hit test info will not be reused.
    */
   void BuildCompositorHitTestInfoIfNeeded(nsIFrame* aFrame,
                                           nsDisplayList* aList,
                                           const bool aBuildNew);
 
-  bool IsBuildingLayerEventRegions();
   bool IsInsidePointerEventsNoneDoc()
   {
     return CurrentPresShellState()->mInsidePointerEventsNoneDoc;
   }
 
   bool GetAncestorHasApzAwareEventHandler() const { return mAncestorHasApzAwareEventHandler; }
   void SetAncestorHasApzAwareEventHandler(bool aValue)
   {
@@ -1074,17 +1066,16 @@ public:
     AutoBuildingDisplayList(nsDisplayListBuilder* aBuilder,
                             nsIFrame* aForChild,
                             const nsRect& aVisibleRect,
                             const nsRect& aDirtyRect,
                             bool aIsRoot)
       : mBuilder(aBuilder),
         mPrevFrame(aBuilder->mCurrentFrame),
         mPrevReferenceFrame(aBuilder->mCurrentReferenceFrame),
-        mPrevLayerEventRegions(aBuilder->mLayerEventRegions),
         mPrevCompositorHitTestInfo(aBuilder->mCompositorHitTestInfo),
         mPrevOffset(aBuilder->mCurrentOffsetToReferenceFrame),
         mPrevVisibleRect(aBuilder->mVisibleRect),
         mPrevDirtyRect(aBuilder->mDirtyRect),
         mPrevAGR(aBuilder->mCurrentAGR),
         mPrevIsAtRootOfPseudoStackingContext(aBuilder->mIsAtRootOfPseudoStackingContext),
         mPrevAncestorHasApzAwareEventHandler(aBuilder->mAncestorHasApzAwareEventHandler),
         mPrevBuildingInvisibleItems(aBuilder->mBuildingInvisibleItems),
@@ -1127,33 +1118,31 @@ public:
       return mCurrentAGRState == AGR_MAYBE;
     }
     void RestoreBuildingInvisibleItemsValue() {
       mBuilder->mBuildingInvisibleItems = mPrevBuildingInvisibleItems;
     }
     ~AutoBuildingDisplayList() {
       mBuilder->mCurrentFrame = mPrevFrame;
       mBuilder->mCurrentReferenceFrame = mPrevReferenceFrame;
-      mBuilder->mLayerEventRegions = mPrevLayerEventRegions;
       mBuilder->mCompositorHitTestInfo = mPrevCompositorHitTestInfo;
       mBuilder->mCurrentOffsetToReferenceFrame = mPrevOffset;
       mBuilder->mVisibleRect = mPrevVisibleRect;
       mBuilder->mDirtyRect = mPrevDirtyRect;
       mBuilder->mCurrentAGR = mPrevAGR;
       mBuilder->mIsAtRootOfPseudoStackingContext = mPrevIsAtRootOfPseudoStackingContext;
       mBuilder->mAncestorHasApzAwareEventHandler = mPrevAncestorHasApzAwareEventHandler;
       mBuilder->mBuildingInvisibleItems = mPrevBuildingInvisibleItems;
       mBuilder->mInInvalidSubtree = mPrevInInvalidSubtree;
     }
   private:
     nsDisplayListBuilder* mBuilder;
     AGRState              mCurrentAGRState;
     const nsIFrame*       mPrevFrame;
     const nsIFrame*       mPrevReferenceFrame;
-    nsDisplayLayerEventRegions* mPrevLayerEventRegions;
     nsDisplayCompositorHitTestInfo* mPrevCompositorHitTestInfo;
     nsPoint               mPrevOffset;
     nsRect                mPrevVisibleRect;
     nsRect                mPrevDirtyRect;
     RefPtr<AnimatedGeometryRoot> mPrevAGR;
     bool                  mPrevIsAtRootOfPseudoStackingContext;
     bool                  mPrevAncestorHasApzAwareEventHandler;
     bool                  mPrevBuildingInvisibleItems;
@@ -1726,18 +1715,16 @@ public:
   void SetHitTestIsForVisibility(bool aHitTestIsForVisibility) {
     mHitTestIsForVisibility = aHitTestIsForVisibility;
   }
 
   /**
    * Represents a region composed of frame/rect pairs.
    * WeakFrames are used to track whether a rect still belongs to the region.
    * Modified frames and rects are removed and re-added to the region if needed.
-   * nsDisplayLayerEventRegions::FrameRects implements the same functionality
-   * with nsIFrames.
    */
   struct WeakFrameRegion {
     std::vector<WeakFrame> mFrames;
     nsTArray<pixman_box32_t> mRects;
 
     void Add(nsIFrame* aFrame, const nsRect& aRect)
     {
       mFrames.emplace_back(aFrame);
@@ -1857,17 +1844,16 @@ private:
     {}
 
     nsIFrame* mFrame;
     uint32_t mUsage;
   };
 
   nsIFrame* const                mReferenceFrame;
   nsIFrame*                      mIgnoreScrollFrame;
-  nsDisplayLayerEventRegions*    mLayerEventRegions;
   nsDisplayCompositorHitTestInfo* mCompositorHitTestInfo;
 
   nsPresArena mPool;
 
   RefPtr<mozilla::dom::Selection> mBoundingSelection;
   AutoTArray<PresShellState,8> mPresShellStates;
   AutoTArray<nsIFrame*,400>    mFramesMarkedForDisplay;
   AutoTArray<nsIFrame*,40>       mFramesMarkedForDisplayIfVisible;
@@ -4831,234 +4817,16 @@ private:
   mozilla::Maybe<mozilla::layers::FrameMetrics::ViewID> mScrollTarget;
   nsRect mArea;
   uint32_t mIndex;
   mozilla::Maybe<int32_t> mOverrideZIndex;
   int32_t mAppUnitsPerDevPixel;
 };
 
 /**
- * A display item that tracks event-sensitive regions which will be set
- * on the ContainerLayer that eventually contains this item.
- *
- * One of these is created for each stacking context and pseudo-stacking-context.
- * It accumulates regions for event targets contributed by the border-boxes of
- * frames in its (pseudo) stacking context. A nsDisplayLayerEventRegions
- * eventually contributes its regions to the PaintedLayer it is placed in by
- * FrameLayerBuilder. (We don't create a display item for every frame that
- * could be an event target (i.e. almost all frames), because that would be
- * high overhead.)
- *
- * We always make leaf layers other than PaintedLayers transparent to events.
- * For example, an event targeting a canvas or video will actually target the
- * background of that element, which is logically in the PaintedLayer behind the
- * CanvasFrame or ImageFrame. We only need to create a
- * nsDisplayLayerEventRegions when an element's background could be in front
- * of a lower z-order element with its own layer.
- */
-class nsDisplayLayerEventRegions final : public nsDisplayItem {
-public:
-  nsDisplayLayerEventRegions(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame, uint32_t aIndex = 0)
-    : nsDisplayItem(aBuilder, aFrame)
-    , mIndex(aIndex)
-  {
-    MOZ_COUNT_CTOR(nsDisplayLayerEventRegions);
-  }
-
-  virtual void Destroy(nsDisplayListBuilder* aBuilder) override
-  {
-    if (!aBuilder->IsRetainingDisplayList()) {
-      nsDisplayItem::Destroy(aBuilder);
-      return;
-    }
-
-    RemoveItemFromFrames(mHitRegion);
-    RemoveItemFromFrames(mMaybeHitRegion);
-    RemoveItemFromFrames(mDispatchToContentHitRegion);
-    RemoveItemFromFrames(mNoActionRegion);
-    RemoveItemFromFrames(mHorizontalPanRegion);
-    RemoveItemFromFrames(mVerticalPanRegion);
-    nsDisplayItem::Destroy(aBuilder);
-  }
-
-  virtual nsRect GetBounds(nsDisplayListBuilder* aBuilder,
-                           bool* aSnap) const override
-  {
-    *aSnap = false;
-    return nsRect();
-  }
-  nsRect GetHitRegionBounds(nsDisplayListBuilder* aBuilder, bool* aSnap)
-  {
-    *aSnap = false;
-    // TODO: This constructs the two regions, but we're also doing the same
-    // work in AccumulateEventRegions. We should avoid doing it twice.
-    return HitRegion().GetBounds().Union(MaybeHitRegion().GetBounds());
-  }
-
-  virtual void ApplyOpacity(nsDisplayListBuilder* aBuilder,
-                            float aOpacity,
-                            const DisplayItemClipChain* aClip) override
-  {
-    NS_ASSERTION(CanApplyOpacity(), "ApplyOpacity should be allowed");
-  }
-  virtual bool CanApplyOpacity() const override
-  {
-    return true;
-  }
-
-  NS_DISPLAY_DECL_NAME("LayerEventRegions", TYPE_LAYER_EVENT_REGIONS)
-
-  // Indicate that aFrame's border-box contributes to the event regions for
-  // this layer. aFrame must have the same reference frame as mFrame.
-  void AddFrame(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame);
-
-  // Indicate that an inactive scrollframe's scrollport should be added to the
-  // dispatch-to-content region, to ensure that APZ lets content create a
-  // displayport.
-  void AddInactiveScrollPort(nsIFrame* aFrame, const nsRect& aRect);
-
-  bool IsEmpty() const;
-
-  int32_t ZIndex() const override;
-  void SetOverrideZIndex(int32_t aZIndex);
-
-  virtual uint32_t GetPerFrameKey() const override
-  {
-    return (mIndex << TYPE_BITS) | nsDisplayItem::GetPerFrameKey();
-  }
-
-  const nsRegion HitRegion()
-  {
-    return nsRegion(mozilla::gfx::ArrayView<pixman_box32_t>(mHitRegion.mBoxes));
-  }
-  const nsRegion MaybeHitRegion()
-  {
-    nsRegion result(mozilla::gfx::ArrayView<pixman_box32_t>(mMaybeHitRegion.mBoxes));
-
-    // Avoid quadratic performance as a result of the region growing to include
-    // an arbitrarily large number of rects, which can happen on some pages.
-    // TODO: It would be nice if we could ask the initial construction above
-    // to include simplification.
-    result.SimplifyOutward(8);
-    return result;
-  }
-  const nsRegion DispatchToContentHitRegion()
-  {
-    nsRegion result(mozilla::gfx::ArrayView<pixman_box32_t>(mDispatchToContentHitRegion.mBoxes));
-
-    // If this frame has touch-action areas, and there were already
-    // touch-action areas from some other element on this same event regions,
-    // then all we know is that there are multiple elements with touch-action
-    // properties. In particular, we don't know what the relationship is
-    // between those elements in terms of DOM ancestry, and so we don't know
-    // how to combine the regions properly. Instead, we just add all the areas
-    // to the dispatch-to-content region, so that the APZ knows to check with
-    // the main thread. XXX we need to come up with a better way to do this,
-    // see bug 1287829.
-    uint32_t touchActionCount =
-      mNoActionRegion.mBoxes.Length() +
-      mHorizontalPanRegion.mBoxes.Length() +
-      mVerticalPanRegion.mBoxes.Length();
-    if (touchActionCount > 1) {
-      result.OrWith(NoActionRegion());
-      result.OrWith(HorizontalPanRegion());
-      result.OrWith(VerticalPanRegion());
-    }
-
-    result.SimplifyOutward(8);
-    return result;
-  }
-  const nsRegion NoActionRegion()
-  {
-    return nsRegion(mozilla::gfx::ArrayView<pixman_box32_t>(mNoActionRegion.mBoxes));
-  }
-  const nsRegion HorizontalPanRegion()
-  {
-    return nsRegion(mozilla::gfx::ArrayView<pixman_box32_t>(mHorizontalPanRegion.mBoxes));
-  }
-  const nsRegion VerticalPanRegion()
-  {
-    return nsRegion(mozilla::gfx::ArrayView<pixman_box32_t>(mVerticalPanRegion.mBoxes));
-  }
-  nsRegion CombinedTouchActionRegion();
-
-  virtual void WriteDebugInfo(std::stringstream& aStream) override;
-
-  // TODO: nsTArray (vector) might not be a great data structure
-  // choice since we need to remove elements from the middle.
-  // Should profile and try figure out the best approach
-  // here.
-  struct FrameRects {
-    void Add(nsIFrame* aFrame, const nsRect& aRect) {
-      mBoxes.AppendElement(nsRegion::RectToBox(aRect));
-      mFrames.AppendElement(aFrame);
-    }
-    void Add(nsIFrame* aFrame, const pixman_box32& aBox) {
-      mBoxes.AppendElement(aBox);
-      mFrames.AppendElement(aFrame);
-    }
-    void Add(const FrameRects& aOther) {
-      mBoxes.AppendElements(aOther.mBoxes);
-      mFrames.AppendElements(aOther.mFrames);
-    }
-
-    bool IsEmpty() const {
-      return mBoxes.IsEmpty();
-    }
-
-    nsTArray<pixman_box32_t> mBoxes;
-    nsTArray<nsIFrame*> mFrames;
-  };
-
-  virtual void RemoveFrame(nsIFrame* aFrame) override;
-
-private:
-  virtual ~nsDisplayLayerEventRegions()
-  {
-    MOZ_COUNT_DTOR(nsDisplayLayerEventRegions);
-  }
-
-  void RemoveItemFromFrames(FrameRects& aFrameRects)
-  {
-    for (nsIFrame* f : aFrameRects.mFrames) {
-      if (f != mFrame) {
-        f->RemoveDisplayItem(this);
-      }
-    }
-  }
-
-  friend bool MergeLayerEventRegions(nsDisplayItem*, nsDisplayItem*);
-
-  // Relative to aFrame's reference frame.
-  // These are the points that are definitely in the hit region.
-  FrameRects mHitRegion;
-  // These are points that may or may not be in the hit region. Only main-thread
-  // event handling can tell for sure (e.g. because complex shapes are present).
-  FrameRects mMaybeHitRegion;
-  // These are points that need to be dispatched to the content thread for
-  // resolution. Always contained in the union of mHitRegion and mMaybeHitRegion.
-  FrameRects mDispatchToContentHitRegion;
-  // These are points where panning is disabled, as determined by the touch-action
-  // property. Always contained in the union of mHitRegion and mMaybeHitRegion.
-  FrameRects mNoActionRegion;
-  // These are points where panning is horizontal, as determined by the touch-action
-  // property. Always contained in the union of mHitRegion and mMaybeHitRegion.
-  FrameRects mHorizontalPanRegion;
-  // These are points where panning is vertical, as determined by the touch-action
-  // property. Always contained in the union of mHitRegion and mMaybeHitRegion.
-  FrameRects mVerticalPanRegion;
-  // If these event regions are for an inactive scroll frame, the z-index of
-  // this display item is overridden to be the largest z-index of the content
-  // in the scroll frame. This ensures that the event regions item remains on
-  // top of the content after sorting items by z-index.
-  mozilla::Maybe<int32_t> mOverrideZIndex;
-  uint32_t mIndex;
-};
-
-/**
  * A class that lets you wrap a display list as a display item.
  *
  * GetUnderlyingFrame() is troublesome for wrapped lists because if the wrapped
  * list has many items, it's not clear which one has the 'underlying frame'.
  * Thus we force the creator to specify what the underlying frame is. The
  * underlying frame should be the root of a stacking context, because sorting
  * a list containing this item will not get at the children.
  *