Don't set scroll client for main frame

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 222 matching lines @@
 #elif OS(ANDROID)
     static const bool platformSupportsCoordinatedScrollbar = true;
     static const bool platformSupportsMainFrameOnly = false;
 #else
     static const bool platformSupportsCoordinatedScrollbar = true;
     static const bool platformSupportsMainFrameOnly = true;
 #endif
     if (!platformSupportsCoordinatedScrollbar)
         return;
 
-    bool isMainFrame = (scrollableArea == static_cast<ScrollableArea*>(m_page->mainFrame()->view()));
+    bool isMainFrame = isForMainFrame(scrollableArea);
     if (!isMainFrame && platformSupportsMainFrameOnly)
         return;
 
     GraphicsLayer* scrollbarGraphicsLayer = orientation == HorizontalScrollbar ? horizontalScrollbarLayerForScrollableArea(scrollableArea) : verticalScrollbarLayerForScrollableArea(scrollableArea);
     if (scrollbarGraphicsLayer) {
         Scrollbar* scrollbar = orientation == HorizontalScrollbar ? scrollableArea->horizontalScrollbar() : scrollableArea->verticalScrollbar();
         if (scrollbar->isCustomScrollbar()) {
             detachScrollbarLayer(scrollbarGraphicsLayer);
             return;
         }
@@ skipping 10 matching lines @@
         scrollbarLayer->layer()->setOpaque(scrollbarGraphicsLayer->contentsOpaque());
 
         setupScrollbarLayer(scrollbarGraphicsLayer, scrollbarLayer, scrollingWebLayerForScrollableArea(scrollableArea));
     } else
         removeWebScrollbarLayer(scrollableArea, orientation);
 }
 
 void ScrollingCoordinator::scrollableAreaScrollLayerDidChange(ScrollableArea* scrollableArea)
 {
     GraphicsLayer* scrollLayer = scrollLayerForScrollableArea(scrollableArea);
-    if (scrollLayer)
-        scrollLayer->setScrollableArea(scrollableArea);
+    if (scrollLayer) {
+        bool isMainFrame = isForMainFrame(scrollableArea);
+        scrollLayer->setScrollableArea(scrollableArea, isMainFrame);
+    }
 
     WebLayer* webLayer = scrollingWebLayerForScrollableArea(scrollableArea);
     if (webLayer) {
         webLayer->setScrollable(true);
         webLayer->setScrollPosition(IntPoint(scrollableArea->scrollPosition() - scrollableArea->minimumScrollPosition()));
         webLayer->setMaxScrollPosition(IntSize(scrollableArea->scrollSize(HorizontalScrollbar), scrollableArea->scrollSize(VerticalScrollbar)));
     }
     if (WebScrollbarLayer* scrollbarLayer = getWebScrollbarLayer(scrollableArea, HorizontalScrollbar))
         setupScrollbarLayer(horizontalScrollbarLayerForScrollableArea(scrollableArea), scrollbarLayer, webLayer);
     if (WebScrollbarLayer* scrollbarLayer = getWebScrollbarLayer(scrollableArea, VerticalScrollbar))
@@ skipping 240 matching lines @@
 GraphicsLayer* ScrollingCoordinator::horizontalScrollbarLayerForScrollableArea(ScrollableArea* scrollableArea)
 {
     return scrollableArea->layerForHorizontalScrollbar();
 }
 
 GraphicsLayer* ScrollingCoordinator::verticalScrollbarLayerForScrollableArea(ScrollableArea* scrollableArea)
 {
     return scrollableArea->layerForVerticalScrollbar();
 }
 
+bool ScrollingCoordinator::isForMainFrame(ScrollableArea* scrollableArea) const
+{
+    return scrollableArea == static_cast<ScrollableArea*>(m_page->mainFrame()->view());

[jamesr, 2013/07/04 00:37:37]

do you need the static cast on the RHS of this for the comparison to compile?
the compiler knows the types on each side so it should be able to do the
mangling necessary (which should only be offset adjustments in case of multiple
inheritance, which we don't have here).

[enne (OOO), 2013/07/04 00:50:17]

You're right.  The compiler will do the right thing here.  Done.

+}
+
 GraphicsLayer* ScrollingCoordinator::scrollLayerForFrameView(FrameView* frameView)
 {
     Frame* frame = frameView->frame();
     if (!frame)
         return 0;
 
     RenderView* renderView = frame->contentRenderer();
     if (!renderView)
         return 0;
     return renderView->compositor()->scrollLayer();
@@ skipping 87 matching lines @@
         stringBuilder.resize(stringBuilder.length() - 2);
     return stringBuilder.toString();
 }
 
 String ScrollingCoordinator::mainThreadScrollingReasonsAsText() const
 {
     return mainThreadScrollingReasonsAsText(mainThreadScrollingReasons());
 }
 
 } // namespace WebCore