Adding mojo MediaSessionClient to support media controls

third_party/WebKit/public/platform/modules/mediasession/media_session.mojom

 // 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.
 
 module blink.mojom;
 
 import "mojo/common/common_custom_types.mojom";
 import "ui/gfx/geometry/mojo/geometry.mojom";
 import "url/mojo/url.mojom";
 
+// Spec: https://wicg.github.io/mediasession/
+enum MediaSessionAction {
+     PLAY,
+     PAUSE,
+     PLAY_PAUSE,
+     PREVIOUS_TRACK,
+     NEXT_TRACK,
+     SEEK_FORWARD,
+     SEEK_BACKWARD,
+};
+
 // Album art in MediaMetadata
 // Spec: https://wicg.github.io/mediasession/
 struct MediaImage {
   url.mojom.Url src;
   mojo.common.mojom.String16 type;
   array<gfx.mojom.Size> sizes;
 };
 
 // MediaMetadata
 // Spec: https://wicg.github.io/mediasession/
 struct MediaMetadata {
   mojo.common.mojom.String16 title;
   mojo.common.mojom.String16 artist;
   mojo.common.mojom.String16 album;
   array<MediaImage> artwork;
 };
 
+interface MediaSessionClient {
+  // Notifies the Blink side that a MediaSessionAction has been fired from the
+  // UI or the platform.
+  DidReceiveAction(MediaSessionAction action);
+};
+
 interface MediaSessionService {
+  // MediaSessionClient interface is used to notify Blink MediaSession of
+  // media control actions.
+  SetClient(MediaSessionClient client);
+
+  // Notifies the browser that the metadata is set, |metadata| will be displayed
+  // on the UI.
   SetMetadata(MediaMetadata? metadata);
+
+  // Notifies the browser that the event handler for |action| has been set,
+  // browser needs to show a media button in the UI or register listeners to the
+  // platform.
+  EnableAction(MediaSessionAction action);
+  // Notifies the browser that the event handler for |action| has been set,
+  // browser needs to hide the media button in the UI and unregister listeners
+  // from the platform.
+  DisableAction(MediaSessionAction action);
 };