cc: Cleanup class/struct forward declarations

cc/trees/layer_tree.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_TREES_LAYER_TREE_H_
 #define CC_TREES_LAYER_TREE_H_
 
 #include <memory>
 #include <unordered_map>
 #include <unordered_set>
@@ skipping 12 matching lines @@
 #include "ui/gfx/geometry/size.h"
 
 namespace base {
 class TimeDelta;
 }  // namespace base
 
 namespace cc {
 
 namespace proto {
 class LayerTree;
-class LayerUpdate;
 }  // namespace proto
 
 class ClientPictureCache;
 class EnginePictureCache;
 class HeadsUpDisplayLayer;
 class Layer;
 class LayerTreeHost;
 class LayerTreeImpl;
 class LayerTreeSettings;
 class MutatorHost;
 struct PendingPageScaleAnimation;
-class UIResourceManager;
-class SwapPromiseManager;
-class SurfaceSequenceGenerator;
 
 class CC_EXPORT LayerTree : public MutatorHostClient {
  public:
   using LayerSet = std::unordered_set<Layer*>;
   using LayerIdMap = std::unordered_map<int, Layer*>;
 
   LayerTree(MutatorHost* mutator_host, LayerTreeHost* layer_tree_host);
   virtual ~LayerTree();
 
   void SetRootLayer(scoped_refptr<Layer> root_layer);
@@ skipping 253 matching lines @@
   // external embedder.
   EnginePictureCache* engine_picture_cache_;
   ClientPictureCache* client_picture_cache_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTree);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_H_