content: Cleanup class/struct forward declarations

content/browser/web_contents/aura/shadow_layer_delegate.h

 // Copyright (c) 2013 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 CONTENT_BROWSER_WEB_CONTENTS_AURA_SHADOW_LAYER_DELEGATE_H_
 #define CONTENT_BROWSER_WEB_CONTENTS_AURA_SHADOW_LAYER_DELEGATE_H_
 
 #include <memory>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "ui/compositor/layer_delegate.h"
 
-namespace aura {
-class Window;
-}
-
 namespace ui {
 class Layer;
 }
 
 namespace content {
 
 // ShadowLayerDelegate takes care of drawing a shadow on the left edge of
 // another layer.
 class ShadowLayerDelegate : public ui::LayerDelegate {
  public:
@@ skipping 11 matching lines @@
   void OnDeviceScaleFactorChanged(float device_scale_factor) override;
 
   std::unique_ptr<ui::Layer> layer_;
 
   DISALLOW_COPY_AND_ASSIGN(ShadowLayerDelegate);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_WEB_CONTENTS_AURA_SHADOW_LAYER_DELEGATE_H_