Bug 1302350 - part2 : provide a method to check whether the agent was started. r=baku

Since the agent is created in beginning in patch1, we need another way to know
whether we have already called notifyStartedPlaying().

MozReview-Commit-ID: 5YNhwEl5Xfp

dom/html/HTMLMediaElement.cpp

@@ -6430,7 +6430,9 @@ HTMLMediaElement::SetAudibleState(bool aAudible)
 void
 HTMLMediaElement::NotifyAudioPlaybackChanged(AudibleChangedReasons aReason)
 {
-  if (!mAudioChannelAgent) {
+  MOZ_ASSERT(mAudioChannelAgent);
+
+  if (!mAudioChannelAgent->IsPlayingStarted()) {
     return;
   }
 
@@ -6554,16 +6556,17 @@ HTMLMediaElement::SetMediaInfo(const MediaInfo& aInfo)
 void
 HTMLMediaElement::AudioCaptureStreamChangeIfNeeded()
 {
-  // Window audio capturing only happens after creating audio channel agent.
-  if (!mAudioChannelAgent) {
-    return;
-  }
+  MOZ_ASSERT(mAudioChannelAgent);
 
   // No need to capture a silence media element.
   if (!HasAudio()) {
     return;
   }
 
+  if (!mAudioChannelAgent->IsPlayingStarted()) {
+    return;
+  }
+
   if (mAudioCapturedByWindow && !mCaptureStreamPort) {
     nsCOMPtr<nsPIDOMWindowInner> window = OwnerDoc()->GetInnerWindow();
     if (!OwnerDoc()->GetInnerWindow()) {