content: Cleanup class/struct forward declarations

content/renderer/gpu/render_widget_compositor_delegate.h

 // Copyright 2015 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_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_DELEGATE_H_
 #define CONTENT_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_DELEGATE_H_
 
 #include <memory>
 #include <vector>
 
 #include "content/common/content_export.h"
 
-namespace blink {
-class WebWidget;
-}
-
 namespace cc {
-class BeginFrameSource;
 class CopyOutputRequest;
 class CompositorFrameSink;
 class SwapPromise;
 }
 
 namespace gfx {
 class Vector2dF;
 }
 
 namespace content {
@@ skipping 56 matching lines @@
   virtual std::unique_ptr<cc::SwapPromise> RequestCopyOfOutputForLayoutTest(
       std::unique_ptr<cc::CopyOutputRequest> request) = 0;
 
  protected:
   virtual ~RenderWidgetCompositorDelegate() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_GPU_RENDER_WIDGET_COMPOSITOR_DELEGATE_H_