bug 839193 - don't exit early in AsyncUsageRunnable::RunInternal r=khuey

dom/indexedDB/IndexedDatabaseManager.cpp

@@ -1798,10 +1798,6 @@ IndexedDatabaseManager::AsyncUsageRunnable::RunInternal()
   IndexedDatabaseManager* mgr = IndexedDatabaseManager::Get();
   NS_ASSERTION(mgr, "This should never fail!");
 
-  if (mCanceled) {
-    return NS_OK;
-  }
-
   switch (mCallbackState) {
     case Pending: {
       NS_NOTREACHED("Should never get here without being dispatched!");