cc: Cleanup class/struct forward declarations

cc/layers/heads_up_display_layer.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_HEADS_UP_DISPLAY_LAYER_H_
 #define CC_LAYERS_HEADS_UP_DISPLAY_LAYER_H_
 
 #include <memory>
 #include <string>
 
 #include "base/macros.h"
 #include "cc/base/cc_export.h"
 #include "cc/layers/layer.h"
 #include "third_party/skia/include/core/SkRefCnt.h"
 #include "third_party/skia/include/core/SkTypeface.h"
 
 namespace cc {
 
-namespace proto {
-class LayerNode;
-}  // namespace proto
-
 class CC_EXPORT HeadsUpDisplayLayer : public Layer {
  public:
   static scoped_refptr<HeadsUpDisplayLayer> Create();
 
   void PrepareForCalculateDrawProperties(
       const gfx::Size& device_viewport, float device_scale_factor);
 
   std::unique_ptr<LayerImpl> CreateLayerImpl(LayerTreeImpl* tree_impl) override;
 
   // Layer overrides.
   void PushPropertiesTo(LayerImpl* layer) override;
 
  protected:
   HeadsUpDisplayLayer();
   bool HasDrawableContent() const override;
 
  private:
   ~HeadsUpDisplayLayer() override;
 
   sk_sp<SkTypeface> typeface_;
 
   DISALLOW_COPY_AND_ASSIGN(HeadsUpDisplayLayer);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_HEADS_UP_DISPLAY_LAYER_H_