Don't set scroll client for main frame

Source/core/platform/graphics/GraphicsLayer.cpp

Index: Source/core/platform/graphics/GraphicsLayer.cpp
diff --git a/Source/core/platform/graphics/GraphicsLayer.cpp b/Source/core/platform/graphics/GraphicsLayer.cpp
index f7ecd9870041b38f723f51c3be37e46cfd088ae2..2973956d6728b773727f0085f837531e3ef16b0c 100644
--- a/Source/core/platform/graphics/GraphicsLayer.cpp
+++ b/Source/core/platform/graphics/GraphicsLayer.cpp
@@ -141,7 +141,6 @@ GraphicsLayer::GraphicsLayer(GraphicsLayerClient* client)
     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);
 }
 
@@ -1336,6 +1335,21 @@ void GraphicsLayer::setLinkHighlight(LinkHighlightClient* 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);