Remove CompositeAndReadback from LayerTreeHost(Impl) and the Proxys.

cc/trees/layer_tree_host_impl.h

Index: cc/trees/layer_tree_host_impl.h
diff --git a/cc/trees/layer_tree_host_impl.h b/cc/trees/layer_tree_host_impl.h
index b9070ac13ae599d46efc792fe896acf2532d3599..85807e6dccda21f4a5f301e0b4012aee40fd5533 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -188,12 +188,11 @@ class CC_EXPORT LayerTreeHostImpl
 
   virtual void ManageTiles();
 
-  // Returns false if problems occured preparing the frame, and we should try
-  // to avoid displaying the frame. If PrepareToDraw is called, DidDrawAllLayers
-  // must also be called, regardless of whether DrawLayers is called between the
-  // two.
-  virtual DrawResult PrepareToDraw(FrameData* frame,
-                                   const gfx::Rect& damage_rect);
+  // Returns DRAW_SUCCESS unless problems occured preparing the frame, and we
+  // should try to avoid displaying the frame. If PrepareToDraw is called,
+  // DidDrawAllLayers must also be called, regardless of whether DrawLayers is
+  // called between the two.
+  virtual DrawResult PrepareToDraw(FrameData* frame);
   virtual void DrawLayers(FrameData* frame, base::TimeTicks frame_begin_time);
   // Must be called if and only if PrepareToDraw was called.
   void DidDrawAllLayers(const FrameData& frame);
@@ -281,8 +280,6 @@ class CC_EXPORT LayerTreeHostImpl
   virtual void WillBeginImplFrame(const BeginFrameArgs& args);
   void DidModifyTilePriorities();
 
-  void Readback(void* pixels, const gfx::Rect& rect_in_device_viewport);
-
   LayerTreeImpl* active_tree() { return active_tree_.get(); }
   const LayerTreeImpl* active_tree() const { return active_tree_.get(); }
   LayerTreeImpl* pending_tree() { return pending_tree_.get(); }