anchor.diff:      }
     }
   
  +  static handleSpawnWorkerRequest(msg) {
  +    var replyPort = msg['replyPort'];
  +    spawn(msg['functionName'], msg['uri'],
  +          msg['args'], msg['msg'],
  +          false, msg['isSpawnUri'], msg['startPaused']).then((msg) {
  +      replyPort.send(msg);
  +    }, onError: (String errorMessage) {
  +      replyPort.send([_SPAWN_FAILED_SIGNAL, errorMessage]);
  +    });
  +  }
  +
     /** Log a message, forwarding to the main [_Manager] if appropriate. */
     static _log(msg) {
       if (_globalState.isWorker) {
  
positive.code:         _globalState.topEventLoop.run();
          break;
        case 'spawn-worker':
          var replyPort = msg['replyPort'];
          spawn(msg['functionName'], msg['uri'],
                msg['args'], msg['msg'],
                false, msg['isSpawnUri'], msg['startPaused']).then((msg) {
            replyPort.send(msg);
          }, onError: (String errorMessage) {
            replyPort.send([_SPAWN_FAILED_SIGNAL, errorMessage]);
          });
          break;
        case 'message':
          SendPort port = msg['port'];
  
negative.code: /// when 'dart:isolate' has been imported.
  class IsolateNatives {
  
    // We set [enableSpawnWorker] to true (not null) when calling isolate
    // primitives that require support for spawning workers. The field starts out
    // by being null, and dart2js' type inference will track if it can have a
    // non-null value. So by testing if this value is not null, we generate code
    // that dart2js knows is dead when worker support isn't needed.
    // TODO(herhut): Initialize this to false when able to track compile-time
    // constants.
    static var enableSpawnWorker;
  
    static String thisScript = computeThisScript();
  
    /// Associates an ID with a native worker object.
  