Bug 1308862 - Null check for the innerWindow. r=jwwang

MozReview-Commit-ID: DXrN3cnqV7U

--HG--
extra : rebase_source : a77e55182e9265ebec8a42d3770df7c41c69b286

dom/html/HTMLTrackElement.cpp

@@ -126,11 +126,14 @@ NS_IMPL_ISUPPORTS(WindowDestroyObserver, nsIObserver);
 HTMLTrackElement::HTMLTrackElement(already_AddRefed<mozilla::dom::NodeInfo>& aNodeInfo)
   : nsGenericHTMLElement(aNodeInfo)
   , mLoadResourceDispatched(false)
+  , mWindowDestroyObserver(nullptr)
 {
   nsISupports* parentObject = OwnerDoc()->GetParentObject();
   NS_ENSURE_TRUE_VOID(parentObject);
   nsCOMPtr<nsPIDOMWindowInner> window = do_QueryInterface(parentObject);
-  mWindowDestroyObserver = new WindowDestroyObserver(this, window->WindowID());
+  if (window) {
+    mWindowDestroyObserver = new WindowDestroyObserver(this, window->WindowID());
+  }
 }
 
 HTMLTrackElement::~HTMLTrackElement()