1 files changed, 15 insertions, 0 deletions
diff --git a/gfx/layers/apz/src/APZCTreeManager.cpp b/gfx/layers/apz/src/APZCTreeManager.cpp
index f54326360..00eb3f183 100644
--- a/gfx/layers/apz/src/APZCTreeManager.cpp
+++ b/gfx/layers/apz/src/APZCTreeManager.cpp
@@ -85,6 +85,21 @@ struct APZCTreeManager::TreeBuildingState {
   std::map<ScrollableLayerGuid, AsyncPanZoomController*> mApzcMap;
 };
 
+// Returns whether or not a wheel event action will be (or was) performed by
+// APZ. If this returns true, the event must not perform a synchronous
+// scroll.
+//
+// Even if this returns false, all wheel events in APZ-aware widgets must
+// be sent through APZ so they are transformed correctly for TabParent.
+static bool
+WillHandleWheelEvent(WidgetWheelEvent* aEvent)
+{
+  return EventStateManager::WheelEventIsScrollAction(aEvent) &&
+         (aEvent->mDeltaMode == nsIDOMWheelEvent::DOM_DELTA_LINE ||
+          aEvent->mDeltaMode == nsIDOMWheelEvent::DOM_DELTA_PIXEL ||
+          aEvent->mDeltaMode == nsIDOMWheelEvent::DOM_DELTA_PAGE);
+}
+
 class APZCTreeManager::CheckerboardFlushObserver : public nsIObserver {
 public:
   NS_DECL_ISUPPORTS