Dispatch scroll wheel events through APZ on Gtk. (bug 1119743, r=nical)

--HG--
extra : rebase_source : c90e3ff64555bb8e121c1605628e2854ea10c823

widget/gtk/nsWindow.cpp

@@ -123,6 +123,8 @@ extern "C" {
 #include "NativeKeyBindings.h"
 #include "nsWindow.h"
 
+#include "mozilla/layers/APZCTreeManager.h"
+
 using namespace mozilla;
 using namespace mozilla::gfx;
 using namespace mozilla::widget;
@@ -3156,8 +3158,19 @@ nsWindow::OnScrollEvent(GdkEventScroll *aEvent)
 
     wheelEvent.time = aEvent->time;
 
-    nsEventStatus status;
-    DispatchEvent(&wheelEvent, status);
+    if (mAPZC) {
+        uint64_t inputBlockId = 0;
+        ScrollableLayerGuid guid;
+
+        nsEventStatus result = mAPZC->ReceiveInputEvent(*wheelEvent.AsWheelEvent(), &guid, &inputBlockId);
+        if (result == nsEventStatus_eConsumeNoDefault) {
+            return;
+        }
+        DispatchEventForAPZ(&wheelEvent, guid, inputBlockId);
+    } else {
+        nsEventStatus status;
+        DispatchEvent(&wheelEvent, status);
+    }
 }
 
 void