Separate VisualViewport layer tree creation from attachment.

third_party/WebKit/Source/core/layout/compositing/PaintLayerCompositor.h

 /*
  * 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 25 matching lines @@
 
 class PaintLayer;
 class DocumentLifecycle;
 class GraphicsLayer;
 class IntPoint;
 class JSONObject;
 class Page;
 class LayoutPart;
 class Scrollbar;
 class ScrollingCoordinator;
+class VisualViewport;
 
 enum CompositingUpdateType {
   CompositingUpdateNone,
   CompositingUpdateAfterGeometryChange,
   CompositingUpdateAfterCompositingInputChange,
   CompositingUpdateRebuildTree,
 };
 
 enum CompositingStateTransitionType {
   NoCompositingStateChange,
@@ skipping 181 matching lines @@
 
   void applyOverlayFullscreenVideoAdjustmentIfNeeded();
 
   void updateContainerSizes();
 
   // Checks the given graphics layer against the compositor's horizontal and
   // vertical scrollbar graphics layers, returning the associated Scrollbar
   // instance if any, else nullptr.
   Scrollbar* graphicsLayerToScrollbar(const GraphicsLayer*) const;
 
+  bool isMainFrame() const;
+  VisualViewport& visualViewport() const;
+
   LayoutView& m_layoutView;
   std::unique_ptr<GraphicsLayer> m_rootContentLayer;
 
   CompositingReasonFinder m_compositingReasonFinder;
 
   CompositingUpdateType m_pendingUpdateType;
 
   bool m_hasAcceleratedCompositing;
   bool m_compositing;
 
@@ skipping 20 matching lines @@
 
   // Layers for overflow controls
   std::unique_ptr<GraphicsLayer> m_layerForHorizontalScrollbar;
   std::unique_ptr<GraphicsLayer> m_layerForVerticalScrollbar;
   std::unique_ptr<GraphicsLayer> m_layerForScrollCorner;
 };
 
 }  // namespace blink
 
 #endif  // PaintLayerCompositor_h