Separate VisualViewport layer tree creation from attachment.

third_party/WebKit/Source/core/frame/VisualViewport.h

 /*
  * Copyright (C) 2013 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 44 matching lines @@
 class IntRect;
 class IntSize;
 class LocalFrame;
 
 // Represents the visual viewport the user is currently seeing the page through.
 // This class corresponds to the InnerViewport on the compositor. It is a
 // ScrollableArea; it's offset is set through the GraphicsLayer <-> CC sync
 // mechanisms. Its contents is the page's main FrameView, which corresponds to
 // the outer viewport. The inner viewport is always contained in the outer
 // viewport and can pan within it.
+//
+// When attached, the tree will look like this:
+//
+// VV::m_rootTransformLayer
+//  +- VV::m_innerViewportContainerLayer
+//     +- VV::m_overscrollElasticityLayer
+//     |   +- VV::m_pageScaleLayer
+//     |       +- VV::m_innerViewportScrollLayer
+//     |           +-- PLC::m_overflowControlsHostLayer
+//     |               +-- PLC::m_containerLayer (fixed pos container)
+//     |                   +-- PLC::m_scrollLayer
+//     |                       +-- PLC::m_rootContentLayer
+//     |                           +-- LayoutView CompositedLayerMapping layers
+//     +- PageOverlay for InspectorOverlay
+//     +- PageOverlay for ColorOverlay
+//     +- PLC::m_layerForHorizontalScrollbar
+//     +- PLC::m_layerForVerticalScrollbar
+//     +- PLC::m_layerForScrollCorner (non-overlay only)
+//
 class CORE_EXPORT VisualViewport final
     : public GarbageCollectedFinalized<VisualViewport>,
       public GraphicsLayerClient,
       public ScrollableArea {
   USING_GARBAGE_COLLECTED_MIXIN(VisualViewport);
 
  public:
   static VisualViewport* create(FrameHost& host) {
     return new VisualViewport(host);
   }
   ~VisualViewport() override;
 
   DECLARE_VIRTUAL_TRACE();
 
-  void attachToLayerTree(GraphicsLayer*);
+  void createLayerTree();
+  void attachLayerTree(GraphicsLayer*);
 
   GraphicsLayer* rootGraphicsLayer() { return m_rootTransformLayer.get(); }
   GraphicsLayer* containerLayer() {
     return m_innerViewportContainerLayer.get();
   }
   GraphicsLayer* scrollLayer() { return m_innerViewportScrollLayer.get(); }
   GraphicsLayer* pageScaleLayer() { return m_pageScaleLayer.get(); }
   GraphicsLayer* overscrollElasticityLayer() {
     return m_overscrollElasticityLayer.get();
   }
@@ skipping 175 matching lines @@
   float m_scale;
   IntSize m_size;
   float m_browserControlsAdjustment;
   float m_maxPageScale;
   bool m_trackPinchZoomStatsForPage;
 };
 
 }  // namespace blink
 
 #endif  // VisualViewport_h