Bug 1271493 Dispatch fetch control runnable even in opt builds. r=mccr8

dom/fetch/Fetch.cpp

@@ -335,7 +335,7 @@ public:
     return true;
   }
 
-  nsresult
+  NS_IMETHOD
   Cancel() override
   {
     // Execute Run anyway to make sure we cleanup our promise proxy to avoid
@@ -403,8 +403,9 @@ WorkerFetchResolver::OnResponseEnd()
     // This can fail if the worker thread is canceled or killed causing
     // the PromiseWorkerProxy to give up its WorkerFeature immediately,
     // allowing the worker thread to become Dead.
-    NS_WARN_IF_FALSE(cr->Dispatch(),
-                     "Failed to dispatch WorkerFetchResponseEndControlRunnable");
+    if (!cr->Dispatch()) {
+      NS_WARNING("Failed to dispatch WorkerFetchResponseEndControlRunnable");
+    }
   }
 }