--- a/gfx/layers/apz/src/APZCTreeManager.cpp
+++ b/gfx/layers/apz/src/APZCTreeManager.cpp
@@ -17,16 +17,17 @@
 #include "mozilla/gfx/GPUParent.h"      // for GPUParent
 #include "mozilla/gfx/Logging.h"        // for gfx::TreeLog
 #include "mozilla/gfx/Point.h"          // for Point
 #include "mozilla/layers/APZThreadUtils.h"  // for AssertOnCompositorThread, etc
 #include "mozilla/layers/AsyncCompositionManager.h" // for ViewTransform
 #include "mozilla/layers/AsyncDragMetrics.h" // for AsyncDragMetrics
 #include "mozilla/layers/CompositorBridgeParent.h" // for CompositorBridgeParent, etc
 #include "mozilla/layers/LayerMetricsWrapper.h"
+#include "mozilla/layers/WebRenderScrollDataWrapper.h"
 #include "mozilla/MouseEvents.h"
 #include "mozilla/mozalloc.h"           // for operator new
 #include "mozilla/TouchEvents.h"
 #include "mozilla/Preferences.h"        // for Preferences
 #include "mozilla/EventStateManager.h"  // for WheelPrefs
 #include "nsDebug.h"                    // for NS_WARNING
 #include "nsPoint.h"                    // for nsIntPoint
 #include "nsThreadUtils.h"              // for NS_IsMainThread
@@ -208,17 +209,17 @@ APZCTreeManager::GetFrameTime()
 
 void
 APZCTreeManager::SetAllowedTouchBehavior(uint64_t aInputBlockId,
                                          const nsTArray<TouchBehaviorFlags> &aValues)
 {
   mInputQueue->SetAllowedTouchBehavior(aInputBlockId, aValues);
 }
 
-template<class ScrollNode> void // ScrollNode is a LayerMetricsWrapper
+template<class ScrollNode> void // ScrollNode is a LayerMetricsWrapper or a WebRenderScrollDataWrapper
 APZCTreeManager::UpdateHitTestingTreeImpl(uint64_t aRootLayerTreeId,
                                           const ScrollNode& aRoot,
                                           bool aIsFirstPaint,
                                           uint64_t aOriginatingLayersId,
                                           uint32_t aPaintSequenceNumber)
 {
   APZThreadUtils::AssertOnCompositorThread();
 
@@ -343,16 +344,28 @@ APZCTreeManager::UpdateHitTestingTree(ui
                                       uint64_t aOriginatingLayersId,
                                       uint32_t aPaintSequenceNumber)
 {
   LayerMetricsWrapper root(aRoot);
   UpdateHitTestingTreeImpl(aRootLayerTreeId, root, aIsFirstPaint,
                            aOriginatingLayersId, aPaintSequenceNumber);
 }
 
+void
+APZCTreeManager::UpdateHitTestingTree(uint64_t aRootLayerTreeId,
+                                      const WebRenderScrollData& aScrollData,
+                                      bool aIsFirstPaint,
+                                      uint64_t aOriginatingLayersId,
+                                      uint32_t aPaintSequenceNumber)
+{
+  WebRenderScrollDataWrapper wrapper(&aScrollData);
+  UpdateHitTestingTreeImpl(aRootLayerTreeId, wrapper, aIsFirstPaint,
+                           aOriginatingLayersId, aPaintSequenceNumber);
+}
+
 // Compute the clip region to be used for a layer with an APZC. This function
 // is only called for layers which actually have scrollable metrics and an APZC.
 template<class ScrollNode> static ParentLayerIntRegion
 ComputeClipRegion(GeckoContentController* aController,
                   const ScrollNode& aLayer)
 {
   ParentLayerIntRegion clipRegion;
   if (aLayer.GetClipRect()) {

--- a/gfx/layers/apz/src/APZCTreeManager.h
+++ b/gfx/layers/apz/src/APZCTreeManager.h
@@ -31,16 +31,17 @@ class APZCTreeManagerParent;
 class CompositorBridgeParent;
 class OverscrollHandoffChain;
 struct OverscrollHandoffState;
 struct FlingHandoffState;
 class LayerMetricsWrapper;
 class InputQueue;
 class GeckoContentController;
 class HitTestingTreeNode;
+class WebRenderScrollData;
 
 /**
  * ****************** NOTE ON LOCK ORDERING IN APZ **************************
  *
  * There are two kinds of locks used by APZ: APZCTreeManager::mTreeLock
  * ("the tree lock") and AsyncPanZoomController::mMonitor ("APZC locks").
  *
  * To avoid deadlock, we impose a lock ordering between these locks, which is:
@@ -123,16 +124,28 @@ public:
    */
   void UpdateHitTestingTree(uint64_t aRootLayerTreeId,
                             Layer* aRoot,
                             bool aIsFirstPaint,
                             uint64_t aOriginatingLayersId,
                             uint32_t aPaintSequenceNumber);
 
   /**
+   * Same as the above UpdateHitTestingTree, except slightly modified to take
+   * the scrolling data passed over PWebRenderBridge instead of the raw layer
+   * tree. This version is used when WebRender is enabled because we don't have
+   * shadow layers in that scenario.
+   */
+  void UpdateHitTestingTree(uint64_t aRootLayerTreeId,
+                            const WebRenderScrollData& aScrollData,
+                            bool aIsFirstPaint,
+                            uint64_t aOriginatingLayersId,
+                            uint32_t aPaintSequenceNumber);
+
+  /**
    * Walk the tree of APZCs and flushes the repaint requests for all the APZCS
    * corresponding to the given layers id. Finally, sends a flush complete
    * notification to the GeckoContentController for the layers id.
    */
   void FlushApzRepaints(uint64_t aLayersId);
 
   /**
    * General handler for incoming input events. Manipulates the frame metrics

--- a/gfx/layers/moz.build
+++ b/gfx/layers/moz.build
@@ -202,16 +202,17 @@ EXPORTS.mozilla.layers += [
     'wr/WebRenderBridgeParent.h',
     'wr/WebRenderCompositableHolder.h',
     'wr/WebRenderDisplayItemLayer.h',
     'wr/WebRenderImageHost.h',
     'wr/WebRenderLayerManager.h',
     'wr/WebRenderLayersLogging.h',
     'wr/WebRenderMessageUtils.h',
     'wr/WebRenderScrollData.h',
+    'wr/WebRenderScrollDataWrapper.h',
     'wr/WebRenderTextureHost.h',
 ]
 
 if CONFIG['MOZ_X11']:
     EXPORTS.mozilla.layers += [
         'basic/TextureClientX11.h',
         'basic/X11TextureSourceBasic.h',
         'composite/X11TextureHost.h',

new file mode 100644
--- /dev/null
+++ b/gfx/layers/wr/WebRenderScrollDataWrapper.h
@@ -0,0 +1,173 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef GFX_WEBRENDERSCROLLDATAWRAPPER_H
+#define GFX_WEBRENDERSCROLLDATAWRAPPER_H
+
+#include "FrameMetrics.h"
+#include "mozilla/layers/WebRenderScrollData.h"
+
+namespace mozilla {
+namespace layers {
+
+/*
+ * This class is a wrapper to walk through a WebRenderScrollData object, with
+ * an exposed API that is template-compatible to LayerMetricsWrapper. This allows
+ * APZ to walk through both layer trees and WebRender scroll metadata structures
+ * without a lot of code duplication.
+ * (Note that not all functions from LayerMetricsWrapper are implemented here,
+ * only the ones we've needed in APZ code so far.)
+ *
+ * One important note here is that this class holds a pointer to the "owning"
+ * WebRenderScrollData. The caller must ensure that this class does not outlive
+ * the owning WebRenderScrollData, or this may result in use-after-free errors.
+ * This class being declared a MOZ_STACK_CLASS should help with that.
+ *
+ * Refer to LayerMetricsWrapper.h for actual documentation on the exposed API.
+ */
+class MOZ_STACK_CLASS WebRenderScrollDataWrapper {
+public:
+  explicit WebRenderScrollDataWrapper(const WebRenderScrollData* aData)
+    : mData(aData)
+  {
+  }
+
+  explicit operator bool() const
+  {
+    // TODO
+    return false;
+  }
+
+  bool IsScrollInfoLayer() const
+  {
+    // TODO
+    return false;
+  }
+
+  WebRenderScrollDataWrapper GetLastChild() const
+  {
+    // TODO
+    return WebRenderScrollDataWrapper(nullptr);
+  }
+
+  WebRenderScrollDataWrapper GetPrevSibling() const
+  {
+    // TODO
+    return WebRenderScrollDataWrapper(nullptr);
+  }
+
+  const ScrollMetadata& Metadata() const
+  {
+    // TODO
+    return *ScrollMetadata::sNullMetadata;
+  }
+
+  const FrameMetrics& Metrics() const
+  {
+    return Metadata().GetMetrics();
+  }
+
+  AsyncPanZoomController* GetApzc() const
+  {
+    // TODO
+    return nullptr;
+  }
+
+  void SetApzc(AsyncPanZoomController* aApzc) const
+  {
+    // TODO
+  }
+
+  const char* Name() const
+  {
+    // TODO
+    return nullptr;
+  }
+
+  gfx::Matrix4x4 GetTransform() const
+  {
+    // TODO
+    return gfx::Matrix4x4();
+  }
+
+  CSSTransformMatrix GetTransformTyped() const
+  {
+    return ViewAs<CSSTransformMatrix>(GetTransform());
+  }
+
+  bool TransformIsPerspective() const
+  {
+    // TODO
+    return false;
+  }
+
+  EventRegions GetEventRegions() const
+  {
+    // TODO
+    return EventRegions();
+  }
+
+  Maybe<uint64_t> GetReferentId() const
+  {
+    // TODO
+    return Nothing();
+  }
+
+  Maybe<ParentLayerIntRect> GetClipRect() const
+  {
+    // TODO
+    return Nothing();
+  }
+
+  EventRegionsOverride GetEventRegionsOverride() const
+  {
+    // TODO
+    return EventRegionsOverride::NoOverride;
+  }
+
+  ScrollDirection GetScrollbarDirection() const
+  {
+    // TODO
+    return ScrollDirection::NONE;
+  }
+
+  FrameMetrics::ViewID GetScrollbarTargetContainerId() const
+  {
+    // TODO
+    return 0;
+  }
+
+  int32_t GetScrollThumbLength() const
+  {
+    // TODO
+    return 0;
+  }
+
+  bool IsScrollbarContainer() const
+  {
+    // TODO
+    return false;
+  }
+
+  FrameMetrics::ViewID GetFixedPositionScrollContainerId() const
+  {
+    // TODO
+    return 0;
+  }
+
+  const void* GetLayer() const
+  {
+    // TODO
+    return nullptr;
+  }
+
+private:
+  const WebRenderScrollData* mData;
+};
+
+} // namespace layers
+} // namespace mozilla
+
+#endif /* GFX_WEBRENDERSCROLLDATAWRAPPER_H */