Bug 1239899. Part 2 - per spec. await a stable state to pause the element when it is removed from the document. r=cpearce

MozReview-Commit-ID: BCCWgXmUchU

dom/html/HTMLMediaElement.cpp

@@ -3653,16 +3653,21 @@ void HTMLMediaElement::UnbindFromTree(bool aDeep,
 {
   mUnboundFromTree = true;
 
-  if (!mPaused && mNetworkState != nsIDOMHTMLMediaElement::NETWORK_EMPTY) {
-    Pause();
-  }
-
   nsGenericHTMLElement::UnbindFromTree(aDeep, aNullParent);
 
   if (mDecoder) {
     MOZ_ASSERT(IsHidden());
     mDecoder->NotifyOwnerActivityChanged(false);
   }
+
+  RefPtr<HTMLMediaElement> self(this);
+  nsCOMPtr<nsIRunnable> task = NS_NewRunnableFunction([self] () {
+    if (self->mUnboundFromTree &&
+        self->mNetworkState != nsIDOMHTMLMediaElement::NETWORK_EMPTY) {
+      self->Pause();
+    }
+  });
+  RunInStableState(task);
 }
 
 /* static */