Bug 1590579 - part2 : update controller's audible state when it starts. r=chunmin

Everytime when we start a controller, we should also update its audible state correctly, in order to request audio focus correctly.

Differential Revision: https://phabricator.services.mozilla.com/D50151

dom/html/HTMLMediaElement.cpp

@@ -1165,6 +1165,9 @@ class HTMLMediaElement::AudioChannelAgentCallback final
     }
 
     NotifyMediaStarted(mAudioChannelAgent->WindowID());
+    NotifyMediaAudibleChanged(
+        mAudioChannelAgent->WindowID(),
+        mIsOwnerAudible == AudioChannelService::AudibleState::eAudible);
     mAudioChannelAgent->PullInitialUpdate();
   }