Bug 1656398 - part5 : add event handler `onplaybackstatechange`. r=chunmin

Differential Revision: https://phabricator.services.mozilla.com/D86626

dom/chrome-webidl/MediaController.webidl

@@ -41,6 +41,7 @@ interface MediaController : EventTarget {
 
   attribute EventHandler onactivated;
   attribute EventHandler ondeactivated;
+  attribute EventHandler onplaybackstatechange;
   attribute EventHandler onpositionstatechange;
   attribute EventHandler onsupportedkeyschange;
 

dom/media/mediacontrol/MediaController.cpp

@@ -420,6 +420,7 @@ void MediaController::HandleActualPlaybackStateChanged() {
   if (RefPtr<MediaControlService> service = MediaControlService::GetService()) {
     service->NotifyControllerPlaybackStateChanged(this);
   }
+  DispatchAsyncEvent(u"playbackstatechange"_ns);
 }
 
 void MediaController::UpdateActivatedStateIfNeeded() {

dom/media/mediacontrol/MediaController.h

@@ -92,6 +92,7 @@ class MediaController final : public DOMEventTargetHelper,
   IMPL_EVENT_HANDLER(activated);
   IMPL_EVENT_HANDLER(deactivated);
   IMPL_EVENT_HANDLER(supportedkeyschange);
+  IMPL_EVENT_HANDLER(playbackstatechange);
   IMPL_EVENT_HANDLER(positionstatechange);
 
   // IMediaController's methods

xpcom/ds/StaticAtoms.py

@@ -2385,6 +2385,7 @@ STATIC_ATOMS = [
     # Media Controller
     Atom("onactivated", "onactivated"),
     Atom("ondeactivated", "ondeactivated"),
+    Atom("onplaybackstatechange", "onplaybackstatechange"),
     Atom("onpositionstatechange", "onpositionstatechange"),
     Atom("onsupportedkeyschange", "onsupportedkeyschange"),