cc: Make LayerTreeImpl dump layer list to FrameViewer and Devtools

cc/trees/layer_tree_host.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_TREES_LAYER_TREE_HOST_H_
 #define CC_TREES_LAYER_TREE_HOST_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 129 matching lines @@
   void DidInitializeOutputSurface();
   void DidFailToInitializeOutputSurface();
   virtual std::unique_ptr<LayerTreeHostImpl> CreateLayerTreeHostImpl(
       LayerTreeHostImplClient* client);
   void DidLoseOutputSurface();
   bool output_surface_lost() const { return output_surface_lost_; }
   void DidCommitAndDrawFrame() { client_->DidCommitAndDrawFrame(); }
   void DidCompleteSwapBuffers() { client_->DidCompleteSwapBuffers(); }
   bool UpdateLayers();
 
-  LayerListIterator<Layer> begin();
-  LayerListIterator<Layer> end();
-  const LayerListIterator<Layer> begin() const;
-  const LayerListIterator<Layer> end() const;
+  LayerListIterator<Layer> begin() const;
+  LayerListIterator<Layer> end() const;
   LayerListReverseIterator<Layer> rbegin();
   LayerListReverseIterator<Layer> rend();
 
   // Called when the compositor completed page scale animation.
   void DidCompletePageScaleAnimation();
 
   LayerTreeHostClient* client() { return client_; }
   const base::WeakPtr<InputHandler>& GetInputHandler() {
     return input_handler_weak_ptr_;
   }
@@ skipping 431 matching lines @@
 
   uint32_t surface_id_namespace_;
   uint32_t next_surface_sequence_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHost);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_H_