content: Cleanup class/struct forward declarations

content/renderer/media/renderer_gpu_video_accelerator_factories.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_RENDERER_MEDIA_RENDERER_GPU_VIDEO_ACCELERATOR_FACTORIES_H_
 #define CONTENT_RENDERER_MEDIA_RENDERER_GPU_VIDEO_ACCELERATOR_FACTORIES_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/unguessable_token.h"
 #include "cc/output/buffer_to_texture_target_map.h"
 #include "content/child/thread_safe_sender.h"
 #include "content/common/content_export.h"
 #include "media/renderers/gpu_video_accelerator_factories.h"
 #include "ui/gfx/geometry/size.h"
 
-namespace base {
-class WaitableEvent;
-}
-
 namespace gpu {
 class GpuChannelHost;
 class GpuMemoryBufferManager;
 }
 
 namespace content {
 class ContextProviderCommandBuffer;
 
 // Glue code to expose functionality needed by media::GpuVideoAccelerator to
 // RenderViewImpl.  This class is entirely an implementation detail of
@@ skipping 94 matching lines @@
 
   // For sending requests to allocate shared memory in the Browser process.
   scoped_refptr<ThreadSafeSender> thread_safe_sender_;
 
   DISALLOW_COPY_AND_ASSIGN(RendererGpuVideoAcceleratorFactories);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_RENDERER_GPU_VIDEO_ACCELERATOR_FACTORIES_H_