ui: Cleanup class/struct forward declarations

content/renderer/media/media_devices_listener_impl.h

Index: content/renderer/media/media_devices_listener_impl.h
diff --git a/content/renderer/media/media_devices_listener_impl.h b/content/renderer/media/media_devices_listener_impl.h
new file mode 100644
index 0000000000000000000000000000000000000000..5198457a6c87620a77e5214a685e5c61e78d24e3
--- /dev/null
+++ b/content/renderer/media/media_devices_listener_impl.h
@@ -0,0 +1,42 @@
+// Copyright 2016 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_MEDIA_DEVICES_LISTENER_IMPL_H_
+#define CONTENT_RENDERER_MEDIA_MEDIA_DEVICES_LISTENER_IMPL_H_
+
+#include "base/macros.h"
+#include "base/threading/thread_checker.h"
+#include "content/common/content_export.h"
+#include "content/common/media/media_devices.h"
+#include "content/common/media/media_devices.mojom.h"
+
+namespace content {
+
+// This class implements a Mojo object that receives notifications about changes
+// in the set of media devices for a given frame.
+class CONTENT_EXPORT MediaDevicesListenerImpl
+    : public ::mojom::MediaDevicesListener {
+ public:
+  static void Create(int render_frame_id,
+                     ::mojom::MediaDevicesListenerRequest request);
+  explicit MediaDevicesListenerImpl(int render_frame_id);
+  ~MediaDevicesListenerImpl() override;
+
+  // ::mojom::MediaDevicesListener implementation.
+  void OnDevicesChanged(MediaDeviceType type,
+                        uint32_t subscription_id,
+                        const MediaDeviceInfoArray& device_infos) override;
+
+ private:
+  // Used for DCHECKs so methods calls won't execute in the wrong thread.
+  base::ThreadChecker thread_checker_;
+
+  int render_frame_id_;
+
+  DISALLOW_COPY_AND_ASSIGN(MediaDevicesListenerImpl);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_MEDIA_DEVICES_LISTENER_IMPL_H_