cc : Fix layer transform changed tracking bug

cc/layers/layer_impl.cc

 // 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.
 
 #include "cc/layers/layer_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 675 matching lines @@
   if (LayerPropertyChanged())
     NoteLayerPropertyChanged();
   for (size_t i = 0; i < children_.size(); ++i)
     children_[i]->PushLayerPropertyChangedForSubtreeInternal();
 }
 
 void LayerImpl::PushLayerPropertyChangedForSubtree() {
   // We need to update property trees first as layer property can change
   // when its corresponsing property tree node changes.
   PropertyTrees* property_trees = layer_tree_impl()->property_trees();
-  EffectTree effect_tree = property_trees->effect_tree;
-  TransformTree transform_tree = property_trees->transform_tree;
+  EffectTree& effect_tree = property_trees->effect_tree;
+  TransformTree& transform_tree = property_trees->transform_tree;
   for (int i = 1; i < static_cast<int>(effect_tree.size()); ++i) {
     EffectNode* node = effect_tree.Node(i);
     EffectNode* parent_node = effect_tree.parent(node);
     effect_tree.UpdateEffectChanged(node, parent_node);
   }
   for (int i = 1; i < static_cast<int>(transform_tree.size()); ++i) {
     TransformNode* node = transform_tree.Node(i);
     TransformNode* parent_node = transform_tree.parent(node);
     TransformNode* source_node = transform_tree.Node(node->data.source_node_id);
     transform_tree.UpdateTransformChanged(node, parent_node, source_node);
@@ skipping 874 matching lines @@
            .layer_transforms_should_scale_layer_contents) {
     return default_scale;
   }
 
   gfx::Vector2dF transform_scales = MathUtil::ComputeTransform2dScaleComponents(
       DrawTransform(), default_scale);
   return std::max(transform_scales.x(), transform_scales.y());
 }
 
 }  // namespace cc