anchor.diff:      bool isWindowDefined = globalWindow != null;
       bool isWorkerDefined = globalWorker != null;
   
  +    // `isWorker` must be initialized now, since `IsolateNatives.thisScript`
  +    // may access it.
       isWorker = !isWindowDefined && globalPostMessageDefined;
       supportsWorkers = isWorker
          || (isWorkerDefined && IsolateNatives.thisScript != null);
  
positive.code:   /** The entry point given by [startRootIsolate]. */
    final Function entry;
  
    _Manager(this.entry) {
      _nativeDetectEnvironment();
      topEventLoop = new _EventLoop();
      isolates = new Map<int, _IsolateContext>();
  
negative.code:     }
      // A worker has no script tag - so get an url from a stack-trace.
      if (_globalState.isWorker) return computeThisScriptFromTrace();
      // An isolate that doesn't support workers, but doesn't have a
      // currentScript either. This is most likely a Chrome extension.
      return null;
    }
  
  