Bug 1627999 - part4 : listen to the playback change from the event source. r=bryce

This patch will do :
- listen to the playback change from the event source directly

The advantage of doing so :
- more close to the real situation because the event source is where we decide the information that should be displayed the virtual control interface

Differential Revision: https://phabricator.services.mozilla.com/D72498

dom/media/mediacontrol/MediaControlKeysManager.cpp

@@ -102,6 +102,12 @@ void MediaControlKeysManager::SetPlaybackState(
   }
   mPlaybackState = aState;
   LOG_INFO("playbackState=%s", ToMediaSessionPlaybackStateStr(mPlaybackState));
+  if (StaticPrefs::media_mediacontrol_testingevents_enabled()) {
+    if (nsCOMPtr<nsIObserverService> obs = services::GetObserverService()) {
+      obs->NotifyObservers(nullptr, "media-displayed-playback-changed",
+                           nullptr);
+    }
+  }
 }
 
 MediaSessionPlaybackState MediaControlKeysManager::GetPlaybackState() const {

dom/media/mediacontrol/MediaControlService.cpp

@@ -317,12 +317,6 @@ void MediaControlService::ControllerManager::MainControllerPlaybackStateChanged(
     MediaSessionPlaybackState aState) {
   MOZ_ASSERT(NS_IsMainThread());
   mSource->SetPlaybackState(aState);
-  if (StaticPrefs::media_mediacontrol_testingevents_enabled()) {
-    if (nsCOMPtr<nsIObserverService> obs = services::GetObserverService()) {
-      obs->NotifyObservers(nullptr, "main-media-controller-playback-changed",
-                           nullptr);
-    }
-  }
 }
 
 void MediaControlService::ControllerManager::MainControllerMetadataChanged(

dom/media/mediacontrol/tests/browser_media_control_keys_event.js

@@ -56,7 +56,7 @@ add_task(async function testPlayPause() {
  * The following are helper functions.
  */
 function generateMediaControlKeyEvent(event) {
-  const playbackStateChanged = waitUntilMainMediaControllerPlaybackChanged();
+  const playbackStateChanged = waitUntilDisplayedPlaybackChanged();
   ChromeUtils.generateMediaControlKeysTestEvent(event);
   return playbackStateChanged;
 }

dom/media/mediacontrol/tests/head.js

@@ -30,7 +30,7 @@ async function createTabAndLoad(url, inputWindow = null) {
  *         and change its playback state.
  */
 function generateMediaControlKeyEvent(event) {
-  const playbackStateChanged = waitUntilMainMediaControllerPlaybackChanged();
+  const playbackStateChanged = waitUntilDisplayedPlaybackChanged();
   ChromeUtils.generateMediaControlKeysTestEvent(event);
   return playbackStateChanged;
 }
@@ -59,10 +59,7 @@ function playMedia(tab, elementId) {
       return video.play();
     }
   );
-  return Promise.all([
-    playPromise,
-    waitUntilMainMediaControllerPlaybackChanged(),
-  ]);
+  return Promise.all([playPromise, waitUntilDisplayedPlaybackChanged()]);
 }
 
 /**
@@ -90,10 +87,7 @@ function pauseMedia(tab, elementId) {
       video.pause();
     }
   );
-  return Promise.all([
-    pausePromise,
-    waitUntilMainMediaControllerPlaybackChanged(),
-  ]);
+  return Promise.all([pausePromise, waitUntilDisplayedPlaybackChanged()]);
 }
 
 /**
@@ -222,14 +216,14 @@ function isCurrentMetadataEqualTo(metadata) {
 
 /**
  * Wait until the main media controller changes its playback state, we would
- * observe that by listening for `main-media-controller-playback-changed`
+ * observe that by listening for `media-displayed-playback-changed`
  * notification.
  *
  * @return {Promise}
- *         Resolve when observing `main-media-controller-playback-changed`
+ *         Resolve when observing `media-displayed-playback-changed`
  */
-function waitUntilMainMediaControllerPlaybackChanged() {
-  return BrowserUtils.promiseObserved("main-media-controller-playback-changed");
+function waitUntilDisplayedPlaybackChanged() {
+  return BrowserUtils.promiseObserved("media-displayed-playback-changed");
 }
 
 /**