content: Cleanup class/struct forward declarations

content/browser/compositor/software_output_device_mac.h

 // Copyright 2014 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_COMPOSITOR_SOFTWARE_OUTPUT_DEVICE_MAC_H_
 #define CONTENT_BROWSER_COMPOSITOR_SOFTWARE_OUTPUT_DEVICE_MAC_H_
 
 #include <IOSurface/IOSurface.h>
 
 #include "base/mac/scoped_cftyperef.h"
 #include "base/macros.h"
 #include "cc/output/software_output_device.h"
 #include "third_party/skia/include/core/SkRefCnt.h"
 #include "third_party/skia/include/core/SkRegion.h"
 #include "ui/gfx/vsync_provider.h"
 
 class SkCanvas;
 
-namespace gfx {
-class Canvas;
-}
-
 namespace ui {
 class Compositor;
 }
 
 namespace content {
 
 class SoftwareOutputDeviceMac :
     public cc::SoftwareOutputDevice,
     public gfx::VSyncProvider {
  public:
@@ skipping 36 matching lines @@
   std::unique_ptr<SkCanvas> canvas_;
 
   gfx::VSyncProvider::UpdateVSyncCallback update_vsync_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(SoftwareOutputDeviceMac);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_COMPOSITOR_SOFTWARE_OUTPUT_DEVICE_MAC_H_