content: Cleanup class/struct forward declarations

content/browser/media/capture/desktop_capture_device.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_MEDIA_CAPTURE_DESKTOP_CAPTURE_DEVICE_H_
 #define CONTENT_BROWSER_MEDIA_CAPTURE_DESKTOP_CAPTURE_DEVICE_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/threading/thread.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/desktop_media_id.h"
 #include "media/capture/video/video_capture_device.h"
 #include "ui/gfx/native_widget_types.h"
 
 namespace base {
-class SingleThreadTaskRunner;
 class Thread;
 }  // namespace base
 
 namespace webrtc {
 class DesktopCapturer;
 }  // namespace webrtc
 
 namespace content {
 
 // DesktopCaptureDevice implements VideoCaptureDevice for screens and windows.
@@ skipping 27 matching lines @@
 
   base::Thread thread_;
   std::unique_ptr<Core> core_;
 
   DISALLOW_COPY_AND_ASSIGN(DesktopCaptureDevice);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_MEDIA_CAPTURE_DESKTOP_CAPTURE_DEVICE_H_