Bug 750258. Ensure that MediaStreamListener::NotifyBlockingChanged is always called for a new listener, and similar for NotifyFinished called on an already-finished stream. Rely on this to set readyState correctly for media elements consuming a stream. r=jesup,cpearce

content/html/content/src/nsHTMLMediaElement.cpp

@@ -2645,7 +2645,11 @@ void nsHTMLMediaElement::ResourceLoaded()
   mNetworkState = nsIDOMHTMLMediaElement::NETWORK_IDLE;
   AddRemoveSelfReference();
   if (mReadyState >= nsIDOMHTMLMediaElement::HAVE_METADATA) {
-    ChangeReadyState(nsIDOMHTMLMediaElement::HAVE_ENOUGH_DATA);
+    // MediaStream sources are put into HAVE_CURRENT_DATA state here on setup. If the
+    // stream is not blocked, we will receive a notification that will put it
+    // into HAVE_ENOUGH_DATA state.
+    ChangeReadyState(mStream ? nsIDOMHTMLMediaElement::HAVE_CURRENT_DATA
+                     : nsIDOMHTMLMediaElement::HAVE_ENOUGH_DATA);
   }
   // Ensure a progress event is dispatched at the end of download.
   DispatchAsyncEvent(NS_LITERAL_STRING("progress"));

content/media/MediaStreamGraph.cpp

@@ -1761,6 +1761,17 @@ MediaStream::ChangeExplicitBlockerCount(PRInt32 aDelta)
   GraphImpl()->AppendMessage(new Message(this, aDelta));
 }
 
+void
+MediaStream::AddListenerImpl(already_AddRefed<MediaStreamListener> aListener)
+{
+  MediaStreamListener* listener = *mListeners.AppendElement() = aListener;
+  listener->NotifyBlockingChanged(GraphImpl(),
+    mBlocked.GetAt(GraphImpl()->mCurrentTime) ? MediaStreamListener::BLOCKED : MediaStreamListener::UNBLOCKED);
+  if (mNotifiedFinished) {
+    listener->NotifyFinished(GraphImpl());
+  }
+}
+
 void
 MediaStream::AddListener(MediaStreamListener* aListener)
 {

content/media/MediaStreamGraph.h

@@ -83,6 +83,10 @@ class MediaStreamGraph;
  * reentry into media graph methods is possible, although very much discouraged!
  * You should do something non-blocking and non-reentrant (e.g. dispatch an
  * event to some thread) and return.
+ *
+ * When a listener is first attached, we guarantee to send a NotifyBlockingChanged
+ * callback to notify of the initial blocking state. Also, if a listener is
+ * attached to a stream that has already finished, we'll call NotifyFinished.
  */
 class MediaStreamListener {
 public:
@@ -263,10 +267,7 @@ public:
   {
     mExplicitBlockerCount.SetAtAndAfter(aTime, mExplicitBlockerCount.GetAt(aTime) + aDelta);
   }
-  void AddListenerImpl(already_AddRefed<MediaStreamListener> aListener)
-  {
-    *mListeners.AppendElement() = aListener;
-  }
+  void AddListenerImpl(already_AddRefed<MediaStreamListener> aListener);
   void RemoveListenerImpl(MediaStreamListener* aListener)
   {
     mListeners.RemoveElement(aListener);