cc: Add some more infrastructure for two trees

cc/layer_tree_host_impl.h

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_LAYER_TREE_HOST_IMPL_H_
 #define CC_LAYER_TREE_HOST_IMPL_H_
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time.h"
@@ skipping 185 matching lines @@
     bool isContextLost();
     TileManager* tileManager() { return m_tileManager.get(); }
     Renderer* renderer() { return m_renderer.get(); }
     const RendererCapabilities& rendererCapabilities() const;
 
     bool swapBuffers();
 
     void readback(void* pixels, const gfx::Rect&);
 
     LayerTreeImpl* activeTree() { return m_activeTree.get(); }
+    LayerTreeImpl* pendingTree() { return m_pendingTree.get(); }
 
     // TODO(nduca): Remove these in favor of LayerTreeImpl.
     void setRootLayer(scoped_ptr<LayerImpl>);
     LayerImpl* rootLayer() const;
 
     // Release ownership of the current layer tree and replace it with an empty
     // tree. Returns the root layer of the detached tree.
     scoped_ptr<LayerImpl> detachLayerTree();
 
     LayerImpl* rootScrollLayer() const;
@@ skipping 128 matching lines @@
 
     void animateScrollbarsRecursive(LayerImpl*, base::TimeTicks monotonicTime);
 
     void dumpRenderSurfaces(std::string*, int indent, const LayerImpl*) const;
 
     scoped_ptr<OutputSurface> m_outputSurface;
     scoped_ptr<ResourceProvider> m_resourceProvider;
     scoped_ptr<Renderer> m_renderer;
     scoped_ptr<TileManager> m_tileManager;
 
+    scoped_ptr<LayerTreeImpl> m_pendingTree;
     scoped_ptr<LayerTreeImpl> m_activeTree;
 
     bool m_scrollDeltaIsInViewportSpace;
     LayerTreeSettings m_settings;
     LayerTreeDebugState m_debugState;
     gfx::Size m_layoutViewportSize;
     gfx::Size m_deviceViewportSize;
     float m_deviceScaleFactor;
     bool m_visible;
     bool m_contentsTexturesPurged;
@@ skipping 32 matching lines @@
     size_t m_lastSentMemoryVisibleBytes;
     size_t m_lastSentMemoryVisibleAndNearbyBytes;
     size_t m_lastSentMemoryUseBytes;
 
     DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYER_TREE_HOST_IMPL_H_