--- a/dom/ipc/TabChild.cpp
+++ b/dom/ipc/TabChild.cpp
@@ -1722,20 +1722,17 @@ TabChild::HandleRealMouseButtonEvent(con
   if (aInputBlockId && aEvent.mFlags.mHandledByAPZ) {
     nsCOMPtr<nsIDocument> document(GetDocument());
     pendingLayerization =
       APZCCallbackHelper::SendSetTargetAPZCNotification(mPuppetWidget, document,
                                                         aEvent, aGuid,
                                                         aInputBlockId);
   }
 
-  InputAPZContext context(aGuid, aInputBlockId, nsEventStatus_eIgnore);
-  if (pendingLayerization) {
-    InputAPZContext::SetPendingLayerization();
-  }
+  InputAPZContext context(aGuid, aInputBlockId, nsEventStatus_eIgnore, pendingLayerization);
 
   WidgetMouseEvent localEvent(aEvent);
   localEvent.mWidget = mPuppetWidget;
   APZCCallbackHelper::ApplyCallbackTransform(localEvent, aGuid,
       mPuppetWidget->GetDefaultScale());
   DispatchWidgetEventViaAPZ(localEvent);
 
   if (aInputBlockId && aEvent.mFlags.mHandledByAPZ) {

--- a/gfx/layers/apz/util/InputAPZContext.cpp
+++ b/gfx/layers/apz/util/InputAPZContext.cpp
@@ -7,18 +7,18 @@
 #include "InputAPZContext.h"
 
 namespace mozilla {
 namespace layers {
 
 ScrollableLayerGuid InputAPZContext::sGuid;
 uint64_t InputAPZContext::sBlockId = 0;
 nsEventStatus InputAPZContext::sApzResponse = nsEventStatus_eIgnore;
+bool InputAPZContext::sPendingLayerization = false;
 bool InputAPZContext::sRoutedToChildProcess = false;
-bool InputAPZContext::sPendingLayerization = false;
 
 /*static*/ ScrollableLayerGuid
 InputAPZContext::GetTargetLayerGuid()
 {
   return sGuid;
 }
 
 /*static*/ uint64_t
@@ -28,59 +28,54 @@ InputAPZContext::GetInputBlockId()
 }
 
 /*static*/ nsEventStatus
 InputAPZContext::GetApzResponse()
 {
   return sApzResponse;
 }
 
-/*static*/ void
-InputAPZContext::SetRoutedToChildProcess()
-{
-  sRoutedToChildProcess = true;
-}
-
-/*static*/ void
-InputAPZContext::SetPendingLayerization()
+/*static*/ bool
+InputAPZContext::HavePendingLayerization()
 {
-  sPendingLayerization = true;
-}
-
-InputAPZContext::InputAPZContext(const ScrollableLayerGuid& aGuid,
-                                 const uint64_t& aBlockId,
-                                 const nsEventStatus& aApzResponse)
-  : mOldGuid(sGuid)
-  , mOldBlockId(sBlockId)
-  , mOldApzResponse(sApzResponse)
-  , mOldRoutedToChildProcess(sRoutedToChildProcess)
-  , mOldPendingLayerization(sPendingLayerization)
-{
-  sGuid = aGuid;
-  sBlockId = aBlockId;
-  sApzResponse = aApzResponse;
-  sRoutedToChildProcess = false;
-  sPendingLayerization = false;
-}
-
-InputAPZContext::~InputAPZContext()
-{
-  sGuid = mOldGuid;
-  sBlockId = mOldBlockId;
-  sApzResponse = mOldApzResponse;
-  sRoutedToChildProcess = mOldRoutedToChildProcess;
-  sPendingLayerization = mOldPendingLayerization;
+  return sPendingLayerization;
 }
 
 /*static*/ bool
 InputAPZContext::WasRoutedToChildProcess()
 {
   return sRoutedToChildProcess;
 }
 
-/*static*/ bool
-InputAPZContext::HavePendingLayerization()
+InputAPZContext::InputAPZContext(const ScrollableLayerGuid& aGuid,
+                                 const uint64_t& aBlockId,
+                                 const nsEventStatus& aApzResponse,
+                                 bool aPendingLayerization)
+  : mOldGuid(sGuid)
+  , mOldBlockId(sBlockId)
+  , mOldApzResponse(sApzResponse)
+  , mOldPendingLayerization(sPendingLayerization)
+  , mOldRoutedToChildProcess(sRoutedToChildProcess)
 {
-  return sPendingLayerization;
+  sGuid = aGuid;
+  sBlockId = aBlockId;
+  sApzResponse = aApzResponse;
+  sPendingLayerization = aPendingLayerization;
+  sRoutedToChildProcess = false;
+}
+
+InputAPZContext::~InputAPZContext()
+{
+  sGuid = mOldGuid;
+  sBlockId = mOldBlockId;
+  sApzResponse = mOldApzResponse;
+  sPendingLayerization = mOldPendingLayerization;
+  sRoutedToChildProcess = mOldRoutedToChildProcess;
+}
+
+/*static*/ void
+InputAPZContext::SetRoutedToChildProcess()
+{
+  sRoutedToChildProcess = true;
 }
 
 } // namespace layers
 } // namespace mozilla

--- a/gfx/layers/apz/util/InputAPZContext.h
+++ b/gfx/layers/apz/util/InputAPZContext.h
@@ -8,48 +8,64 @@
 #define mozilla_layers_InputAPZContext_h
 
 #include "FrameMetrics.h"
 #include "mozilla/EventForwards.h"
 
 namespace mozilla {
 namespace layers {
 
-// InputAPZContext is used to communicate the ScrollableLayerGuid,
-// input block ID, APZ response from nsIWidget to RenderFrameParent.
-// It is conceptually attached to any WidgetInputEvent
-// that has been processed by APZ directly from a widget.
+// InputAPZContext is used to communicate various pieces of information
+// around the codebase without having to plumb it through lots of functions
+// and codepaths. Conceptually it is attached to a WidgetInputEvent that is
+// relevant to APZ.
+//
+// There are two types of information bits propagated using this class. One
+// type is propagated "downwards" (from a process entry point like nsBaseWidget
+// or TabChild) into deeper code that is run during complicated operations
+// like event dispatch. The other type is information that is propagated
+// "upwards", from the deeper code back to the entry point.
 class MOZ_STACK_CLASS InputAPZContext
 {
 private:
+  // State that is propagated downwards from InputAPZContext creation into
+  // "deeper" code.
   static ScrollableLayerGuid sGuid;
   static uint64_t sBlockId;
   static nsEventStatus sApzResponse;
-  static bool sRoutedToChildProcess;
   static bool sPendingLayerization;
 
+  // State that is set in deeper code and propagated upwards.
+  static bool sRoutedToChildProcess;
+
 public:
+  // Functions to access downwards-propagated data
   static ScrollableLayerGuid GetTargetLayerGuid();
   static uint64_t GetInputBlockId();
   static nsEventStatus GetApzResponse();
-  static void SetRoutedToChildProcess();
-  static void SetPendingLayerization();
+  static bool HavePendingLayerization();
 
+  // Functions to access upwards-propagated data
+  static bool WasRoutedToChildProcess();
+
+  // Constructor sets the data to be propagated downwards
   InputAPZContext(const ScrollableLayerGuid& aGuid,
                   const uint64_t& aBlockId,
-                  const nsEventStatus& aApzResponse);
+                  const nsEventStatus& aApzResponse,
+                  bool aPendingLayerization = false);
   ~InputAPZContext();
 
-  static bool WasRoutedToChildProcess();
-  static bool HavePendingLayerization();
+  // Functions to set data to be propagated upwards
+  static void SetRoutedToChildProcess();
 
 private:
   ScrollableLayerGuid mOldGuid;
   uint64_t mOldBlockId;
   nsEventStatus mOldApzResponse;
+  bool mOldPendingLayerization;
+
   bool mOldRoutedToChildProcess;
-  bool mOldPendingLayerization;
 };
 
 } // namespace layers
 } // namespace mozilla
 
 #endif /* mozilla_layers_InputAPZContext_h */