cc: Add a main thread LayerListIterator

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 <map>
 #include <set>
 #include <string>
@@ skipping 130 matching lines @@
     property_trees_.is_main_thread = false;
     property_trees_.is_active = IsActiveTree();
     property_trees_.transform_tree.set_source_to_parent_updates_allowed(false);
   }
   PropertyTrees* property_trees() { return &property_trees_; }
 
   void UpdatePropertyTreesForBoundsDelta();
 
   void PushPropertiesTo(LayerTreeImpl* tree_impl);
 
-  LayerListIterator begin();
-  LayerListIterator end();
-  LayerListReverseIterator rbegin();
-  LayerListReverseIterator rend();
+  LayerListIterator<LayerImpl> begin();
+  LayerListIterator<LayerImpl> end();
+  LayerListReverseIterator<LayerImpl> rbegin();
+  LayerListReverseIterator<LayerImpl> rend();
 
   // TODO(thakis): Consider marking this CC_EXPORT once we understand
   // http://crbug.com/575700 better.
   struct ElementLayers {
     // Transform and opacity mutations apply to this layer.
     LayerImpl* main = nullptr;
     // Scroll mutations apply to this layer.
     LayerImpl* scroll = nullptr;
   };
 
@@ skipping 423 matching lines @@
 
   scoped_ptr<PendingPageScaleAnimation> pending_page_scale_animation_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_IMPL_H_