Don't set scroll client for main frame

Source/core/platform/graphics/GraphicsLayer.cpp

 /*
  * Copyright (C) 2009 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 123 matching lines @@
     , m_scrollableArea(0)
 {
 #ifndef NDEBUG
     if (m_client)
         m_client->verifyNotPainting();
 #endif
 
     m_opaqueRectTrackingContentLayerDelegate = adoptPtr(new OpaqueRectTrackingContentLayerDelegate(this));
     m_layer = adoptPtr(Platform::current()->compositorSupport()->createContentLayer(m_opaqueRectTrackingContentLayerDelegate.get()));
     m_layer->layer()->setDrawsContent(m_drawsContent && m_contentsVisible);
-    m_layer->layer()->setScrollClient(this);
     m_layer->setAutomaticallyComputeRasterScale(true);
 }
 
 GraphicsLayer::~GraphicsLayer()
 {
     if (m_linkHighlight) {
         m_linkHighlight->clearCurrentGraphicsLayer();
         m_linkHighlight = 0;
     }
 
@@ skipping 1174 matching lines @@
         return;
     m_layer->layer()->setBackgroundFilters(*webFilters);
 }
 
 void GraphicsLayer::setLinkHighlight(LinkHighlightClient* linkHighlight)
 {
     m_linkHighlight = linkHighlight;
     updateChildList();
 }
 
+void GraphicsLayer::setScrollableArea(ScrollableArea* scrollableArea, bool isMainFrame)
+{
+    if (m_scrollableArea == scrollableArea)
+        return;
+
+    m_scrollableArea = scrollableArea;
+
+    // Main frame scrolling may involve pinch zoom and gets routed through
+    // WebViewImpl explicitly rather than via GraphicsLayer::didScroll.
+    if (isMainFrame)
+        m_layer->layer()->setScrollClient(0);
+    else
+        m_layer->layer()->setScrollClient(this);
+}
+
 void GraphicsLayer::paint(GraphicsContext& context, const IntRect& clip)
 {
     paintGraphicsLayerContents(context, clip);
 }
 
 
 void GraphicsLayer::notifyAnimationStarted(double startTime)
 {
     if (m_client)
         m_client->notifyAnimationStarted(this, startTime);
@@ skipping 15 matching lines @@
 #ifndef NDEBUG
 void showGraphicsLayerTree(const WebCore::GraphicsLayer* layer)
 {
     if (!layer)
         return;
 
     String output = layer->layerTreeAsText(WebCore::LayerTreeIncludesDebugInfo);
     fprintf(stderr, "%s\n", output.utf8().data());
 }
 #endif