Bug 1233171 Cancel channel when ScriptLoader is aborted during service worker script load. r=khuey

dom/workers/ScriptLoader.cpp

@@ -629,6 +629,7 @@ private:
     // If one load info cancels or hits an error, it can race with the start
     // callback coming from another load info.
     if (mCanceledMainThread || !mCacheCreator) {
+      aRequest->Cancel(NS_ERROR_FAILURE);
       return NS_ERROR_FAILURE;
     }