Disentangle updating the ScrollingCoordinator from RenderLayerCompositor

Source/core/page/scrolling/ScrollingCoordinator.cpp

 /*
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 104 matching lines @@
     }
 }
 
 void ScrollingCoordinator::notifyLayoutUpdated()
 {
     m_scrollGestureRegionIsDirty = true;
     m_touchEventTargetRectsAreDirty = true;
     m_shouldScrollOnMainThreadDirty = true;
 }
 
-void ScrollingCoordinator::updateAfterCompositingChange()
+void ScrollingCoordinator::updateAfterCompositingChangeIfNeeded()
 {
-    TRACE_EVENT0("input", "ScrollingCoordinator::updateAfterCompositingChange");
+    if (!shouldUpdateAfterCompositingChange())
+        return;
+
+    TRACE_EVENT0("input", "ScrollingCoordinator::updateAfterCompositingChangeIfNeeded");
 
     if (m_scrollGestureRegionIsDirty) {
         // Compute the region of the page where we can't handle scroll gestures and mousewheel events
         // on the impl thread. This currently includes:
         // 1. All scrollable areas, such as subframes, overflow divs and list boxes, whose composited
         // scrolling are not enabled. We need to do this even if the frame view whose layout was updated
         // is not the main frame.
         // 2. Resize control areas, e.g. the small rect at the right bottom of div/textarea/iframe when
         // CSS property "resize" is enabled.
         // 3. Plugin areas.
@@ skipping 839 matching lines @@
     bool frameIsScrollable = frameView && frameView->isScrollable();
     if (frameIsScrollable != m_wasFrameScrollable)
         return true;
 
     if (WebLayer* scrollLayer = frameView ? toWebLayer(frameView->layerForScrolling()) : 0)
         return blink::WebSize(frameView->contentsSize()) != scrollLayer->bounds();
     return false;
 }
 
 } // namespace WebCore