cc: Cleanup class/struct forward declarations

cc/layers/layer_list_iterator.h

 // Copyright 2016 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_LIST_ITERATOR_H_
 #define CC_LAYERS_LAYER_LIST_ITERATOR_H_
 
 #include <stdlib.h>
 #include <vector>
 
 #include "cc/base/cc_export.h"
 
 namespace cc {
 
-class Layer;
 class LayerImpl;
 
 // Unlike LayerIterator and friends, these iterators are not intended to permit
 // traversing the RSLL. Rather, they visit a collection of LayerImpls in
 // stacking order. All recursive walks over the LayerImpl tree should be
 // switched to use these classes instead as the concept of a LayerImpl tree is
 // deprecated.
 template <typename LayerType>
 class CC_EXPORT LayerListIterator {
  public:
@@ skipping 33 matching lines @@
 
  private:
   void DescendToRightmostInSubtree();
   LayerType* current_layer() { return this->current_layer_; }
   std::vector<size_t>& list_indices() { return this->list_indices_; }
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_LIST_ITERATOR_H_