content: Cleanup class/struct forward declarations

content/public/browser/android/synchronous_compositor.h

 // Copyright 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_PUBLIC_BROWSER_ANDROID_SYNCHRONOUS_COMPOSITOR_H_
 #define CONTENT_PUBLIC_BROWSER_ANDROID_SYNCHRONOUS_COMPOSITOR_H_
 
 #include <stddef.h>
 
 #include <memory>
 
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/time/time.h"
 #include "cc/resources/returned_resource.h"
 #include "content/common/content_export.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/size.h"
 
 class SkCanvas;
 
 namespace cc {
 class CompositorFrame;
-class CompositorFrameAck;
 }
 
 namespace gfx {
 class Point;
 class ScrollOffset;
 class Transform;
 };
 
 namespace content {
 
@@ skipping 83 matching lines @@
   // and if any input animation is active, it should tick now.
   virtual void OnComputeScroll(base::TimeTicks animation_time) = 0;
 
  protected:
   virtual ~SynchronousCompositor() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_ANDROID_SYNCHRONOUS_COMPOSITOR_H_