Bug 1391666 - P2. Reset mWaitingForKey when we have data and autoplay attribute is set r=cpearce

By default, a media element that has never played is in paused mode. As such, we need to reset mWaitingForKey to NOT_WAITING_FOR_KEY otherwise, readyState will never become HAVE_ENOUGH_DATA.

MozReview-Commit-ID: EIi3Crt4zHl

dom/html/HTMLMediaElement.cpp

@@ -5919,11 +5919,15 @@ void HTMLMediaElement::ChangeReadyState(nsMediaReadyState aState)
       mReadyState >= nsIDOMHTMLMediaElement::HAVE_FUTURE_DATA) {
     DispatchAsyncEvent(NS_LITERAL_STRING("canplay"));
     if (!mPaused) {
-      mWaitingForKey = NOT_WAITING_FOR_KEY;
       NotifyAboutPlaying();
     }
   }
 
+  if (mReadyState >= nsIDOMHTMLMediaElement::HAVE_FUTURE_DATA &&
+      (!mPaused || mAutoplaying)) {
+    mWaitingForKey = NOT_WAITING_FOR_KEY;
+  }
+
   CheckAutoplayDataReady();
 
   if (oldState < nsIDOMHTMLMediaElement::HAVE_ENOUGH_DATA &&