Bug 1582508 - part1 : implement 'MediaSessionPlaybackState'. r=webidl,chunmin,Ehsan

Implement `playbackstate`[1] attribute for media session interface.

[1] https://w3c.github.io/mediasession/#dom-mediasession-playbackstate

Differential Revision: https://phabricator.services.mozilla.com/D66338

--HG--
extra : moz-landing-system : lando

dom/media/mediasession/MediaSession.cpp

@@ -39,6 +39,20 @@ void MediaSession::SetMetadata(MediaMetadata* aMetadata) {
   NotifyMetadataUpdated();
 }
 
+void MediaSession::SetPlaybackState(
+    const MediaSessionPlaybackState& aPlaybackState) {
+  if (mDeclaredPlaybackState == aPlaybackState) {
+    return;
+  }
+  mDeclaredPlaybackState = aPlaybackState;
+  // TODO : propagate declared state to the media controller in chrome process
+  // in order to call `media session actions update algorithm`.
+}
+
+MediaSessionPlaybackState MediaSession::PlaybackState() const {
+  return mDeclaredPlaybackState;
+}
+
 void MediaSession::SetActionHandler(MediaSessionAction aAction,
                                     MediaSessionActionHandler* aHandler) {
   size_t index = static_cast<size_t>(aAction);

dom/media/mediasession/MediaSession.h

@@ -39,6 +39,10 @@ class MediaSession final : public nsISupports, public nsWrapperCache {
 
   void SetMetadata(MediaMetadata* aMetadata);
 
+  void SetPlaybackState(const MediaSessionPlaybackState& aPlaybackState);
+
+  MediaSessionPlaybackState PlaybackState() const;
+
   void SetActionHandler(MediaSessionAction aAction,
                         MediaSessionActionHandler* aHandler);
 
@@ -72,6 +76,12 @@ class MediaSession final : public nsISupports, public nsWrapperCache {
   RefPtr<MediaMetadata> mMediaMetadata;
   static const size_t ACTIONS = MediaSessionActionValues::Count;
   RefPtr<MediaSessionActionHandler> mActionHandlers[ACTIONS] = {nullptr};
+
+  // This is used as is a hint for the user agent to determine whether the
+  // browsing context is playing or paused.
+  // https://w3c.github.io/mediasession/#declared-playback-state
+  MediaSessionPlaybackState mDeclaredPlaybackState =
+      MediaSessionPlaybackState::None;
 };
 
 }  // namespace dom

dom/webidl/MediaSession.webidl

@@ -7,7 +7,11 @@
  * https://w3c.github.io/mediasession/#idl-index
  */
 
-// TODO: Implement MediaSessionPlaybackState (bug 1582508)
+enum MediaSessionPlaybackState {
+  "none",
+  "paused",
+  "playing"
+};
 
 // TODO: Implement the missing seek* (bug 1580623) and skipad (bug 1582569) actions
 enum MediaSessionAction {
@@ -24,7 +28,7 @@ callback MediaSessionActionHandler = void(MediaSessionActionDetails details);
 interface MediaSession {
   attribute MediaMetadata? metadata;
 
-  // TODO: attribute MediaSessionPlaybackState playbackState; (bug 1582508)
+  attribute MediaSessionPlaybackState playbackState;
 
   void setActionHandler(MediaSessionAction action, MediaSessionActionHandler? handler);