CC Animations: Establish AnimationHost, AnimationTimeline and AnimationPlayer

cc/trees/layer_tree_impl.h

 // Copyright 2012 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_TREES_LAYER_TREE_IMPL_H_
 #define CC_TREES_LAYER_TREE_IMPL_H_
 
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 223 matching lines @@
   const LayerImplList& RenderSurfaceLayerList() const;
   const Region& UnoccludedScreenSpaceRegion() const;
 
   // These return the size of the root scrollable area and the size of
   // the user-visible scrolling viewport, in CSS layout coordinates.
   gfx::Size ScrollableSize() const;
   gfx::SizeF ScrollableViewportSize() const;
 
   gfx::Rect RootScrollLayerDeviceViewportBounds() const;
 
-  LayerImpl* LayerById(int id);
+  LayerImpl* LayerById(int id) const;
 
   // These should be called by LayerImpl's ctor/dtor.
   void RegisterLayer(LayerImpl* layer);
   void UnregisterLayer(LayerImpl* layer);
 
   size_t NumLayers();
 
   AnimationRegistrar* GetAnimationRegistrar() const;
 
   void PushPersistedState(LayerTreeImpl* pending_tree);
@@ skipping 171 matching lines @@
 
   scoped_ptr<PendingPageScaleAnimation> pending_page_scale_animation_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_IMPL_H_