Add graphics layers for pinch virtual viewport.

Source/core/rendering/RenderLayerCompositor.h

Index: Source/core/rendering/RenderLayerCompositor.h
diff --git a/Source/core/rendering/RenderLayerCompositor.h b/Source/core/rendering/RenderLayerCompositor.h
index 15f73f5570d2c45b41bc9bfef434de26c9650c55..41ba9c55510ed17ab7ad531a38fc09a33675328d 100644
--- a/Source/core/rendering/RenderLayerCompositor.h
+++ b/Source/core/rendering/RenderLayerCompositor.h
@@ -328,8 +328,8 @@ private:
     RootLayerAttachment m_rootLayerAttachment;
 
     // Enclosing clipping layer for iframe content
-    OwnPtr<GraphicsLayer> m_clipLayer;
-    OwnPtr<GraphicsLayer> m_scrollLayer;
+    OwnPtr<GraphicsLayer> m_innerViewportClipLayer;
+    OwnPtr<GraphicsLayer> m_innerViewportScrollLayer;
 
     HashSet<RenderLayer*> m_viewportConstrainedLayers;
     HashSet<RenderLayer*> m_viewportConstrainedLayersNeedingUpdate;
@@ -337,6 +337,11 @@ private:
     // Enclosing layer for overflow controls and the clipping layer
     OwnPtr<GraphicsLayer> m_overflowControlsHostLayer;
 
+    // Layers for pinch virtual viewport layers
+    OwnPtr<GraphicsLayer> m_pageScaleLayer;
+    OwnPtr<GraphicsLayer> m_outerViewportClipLayer;
+    OwnPtr<GraphicsLayer> m_outerViewportScrollLayer;
+
     // Layers for overflow controls
     OwnPtr<GraphicsLayer> m_layerForHorizontalScrollbar;
     OwnPtr<GraphicsLayer> m_layerForVerticalScrollbar;