cc: Move render surface ownership from layers to the effect tree

cc/layers/layer_iterator.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_LAYERS_LAYER_ITERATOR_H_
 #define CC_LAYERS_LAYER_ITERATOR_H_
 
 #include <stddef.h>
 
 #include "cc/base/cc_export.h"
@@ skipping 232 matching lines @@
     }
   }
 
   inline LayerImpl* current_layer() const {
     return current_layer_represents_target_render_surface()
                ? target_render_surface_layer()
                : target_render_surface_children().at(current_layer_index_);
   }
 
   inline bool current_layer_represents_contributing_render_surface() const {
-    return current_layer()->render_surface() &&
-           current_layer()->render_surface() != target_render_surface();
+    RenderSurfaceImpl* render_surface = current_layer()->render_surface();
+    return render_surface && render_surface != target_render_surface();
   }
   inline bool current_layer_represents_target_render_surface() const {
     return current_layer_index_ ==
            LayerIteratorValue::kLayerIndexRepresentingTargetRenderSurface;
   }
 
   inline RenderSurfaceImpl* target_render_surface() const {
     return target_render_surface_layer()->render_surface();
   }
   inline const LayerImplList& target_render_surface_children() const {
@@ skipping 17 matching lines @@
   // Since the iterator must also stop at the layers representing
   // the target surface, this is done by setting the current_layer_index
   // to a value of
   // LayerIteratorValue::kLayerIndexRepresentingTargetRenderSurface.
   size_t current_layer_index_;
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_ITERATOR_H_