Ensure that if FrameView::isScrollable() is false, the assoc WebLayer is, too.

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 134 matching lines @@
         Region shouldHandleScrollGestureOnMainThreadRegion = computeShouldHandleScrollGestureOnMainThreadRegion(m_page->mainFrame(), IntPoint());
         setShouldHandleScrollGestureOnMainThreadRegion(shouldHandleScrollGestureOnMainThreadRegion);
         m_scrollGestureRegionIsDirty = false;
     }
 
     if (m_touchEventTargetRectsAreDirty) {
         updateTouchEventTargetRectsIfNeeded();
         m_touchEventTargetRectsAreDirty = false;
     }
 
-    FrameView* frameView = m_page->mainFrame()->view();
-    bool frameIsScrollable = frameView && frameView->isScrollable();
-    if (m_wasFrameScrollable != frameIsScrollable)
+    if (frameViewIsScrollableIsDirty())
         updateShouldUpdateScrollLayerPositionOnMainThread();
-    m_wasFrameScrollable = frameIsScrollable;
+
+    updateMainFrameIsScrollable();
 
     const FrameTree& tree = m_page->mainFrame()->tree();
     for (const Frame* child = tree.firstChild(); child; child = child->tree().nextSibling()) {
         if (WebLayer* scrollLayer = scrollingWebLayerForScrollableArea(child->view()))
             scrollLayer->setBounds(child->view()->contentsSize());
     }
 }
 
 void ScrollingCoordinator::setLayerIsContainerForFixedPositionLayers(GraphicsLayer* layer, bool enable)
 {
@@ skipping 752 matching lines @@
     return mainThreadScrollingReasonsAsText(m_lastMainThreadScrollingReasons);
 }
 
 bool ScrollingCoordinator::frameViewIsScrollableIsDirty() const
 {
     FrameView* frameView = m_page->mainFrame()->view();
     bool frameIsScrollable = frameView && frameView->isScrollable();
     return frameIsScrollable != m_wasFrameScrollable;
 }
 
+void ScrollingCoordinator::updateMainFrameIsScrollable()
+{
+    FrameView* frameView = m_page->mainFrame()->view();
+    bool frameIsScrollable = frameView && frameView->isScrollable();
+    m_wasFrameScrollable = frameIsScrollable;
+
+    if (!frameView)
+        return;
+
+    if (WebLayer* scrollingWebLayer = scrollingWebLayerForScrollableArea(frameView))
+        scrollingWebLayer->setScrollable(frameIsScrollable);
+}
+
 } // namespace WebCore