Bug 1351087 - part1 : don't register agent for audio without audio track. r=baku

Since we don't want to show media control for media without audio track (eg. GIFV),
it's no need to register audio agent for them.

MozReview-Commit-ID: 22YrMkpNrcP

dom/html/HTMLMediaElement.cpp

@@ -1052,6 +1052,11 @@ private:
       return false;
     }
 
+    // No audio track
+    if (!mOwner->HasAudio()) {
+      return false;
+    }
+
     // A loop always is playing
     if (mOwner->HasAttr(kNameSpaceID_None, nsGkAtoms::loop)) {
       return true;
@@ -7080,6 +7085,7 @@ HTMLMediaElement::SetMediaInfo(const MediaInfo& aInfo)
   const bool oldHasAudio = mMediaInfo.HasAudio();
   mMediaInfo = aInfo;
   if (aInfo.HasAudio() != oldHasAudio) {
+    UpdateAudioChannelPlayingState();
     NotifyAudioPlaybackChanged(
       AudioChannelService::AudibleChangedReasons::eDataAudibleChanged);
   }