(Not for review) Dummy C++ side Custom Controls implementation

chrome/browser/media/router/mojo/media_controller.mojom

Index: chrome/browser/media/router/mojo/media_controller.mojom
diff --git a/chrome/browser/media/router/mojo/media_controller.mojom b/chrome/browser/media/router/mojo/media_controller.mojom
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+// Copyright 2017 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.
+
+module media_router.mojom;
+
+import "chrome/browser/media/router/mojo/media_status.mojom";
+
+// Interface for a controller to change the current state of a media content.
+// This interface should be kept free of details specific to Media Router, so
+// that it can be moved to the media namespace and be reused for other features
+// in the future.
+interface MediaController {
+  // Starts playing the media if it is paused. Is a no-op if not supported by
+  // the media or the media is already playing.
+  Play();
+  // Pauses the media if it is playing. Is a no-op if not supported by the media
+  // or the media is already paused.
+  Pause();
+  // Mutes the media if |mute| is true, and unmutes it if false. Is a no-op if
+  // not supported by the media.
+  SetMute(bool mute);
+  // Changes the current volume of the media, with 1 being the highest and 0
+  // being the lowest/no sound. Does not change the (un)muted state of the
+  // media. Is a no-op if not supported by the media.
+  SetVolume(float volume);
+  // Sets the current playback position in milliseconds. |time| must be less
+  // than or equal to the duration of the media. Is a no-op if the media
+  // doesn't support seeking.
+  Seek(uint32 time);
+  // Sets the observer to be notified whenever there is a change in the status
+  // of the media. There can be at most one observer at a time, and it will be
+  // overwritten each time this method is called.
+  // TODO(takumif): Consider allowing multiple observers to be registered.
+  SetObserver(MediaStatusObserver observer);
+};