anchor.diff:  
   const Symbol _APPENGINE_CONTEXT = #appengine_context;
   
  -ClientContext contextFromRequest(HttpRequest request) {
  -  return appengine_internal.contextFromRequest(request);
  -}
  -
  -Future runAppEngineRaw(AppEngineRequestHandler handler) {
  -  return appengine_internal.runAppEngine(handler);
  -}
  -
  +/**
  + * Starts serving requests coming to this AppEngine application.
  + *
  + * This function will start an HTTP server and will forward new HTTP requests
  + * to [handler].
  + *
  + * The [handler] will be executed inside a new request handler zone for every
  + * new request. This will isolate different requests from each other.
  + * Each [handler] has access to a [ClientContext] using the [context] getter
  + * in this library. It can be used to access appengine services, e.g. memcache.
  + *
  + * In case an uncaught error occurs inside the request handler, the request
  + * will be closed with an "500 Internal Server Error", if possible, and the
  + * given [onError] handler will be called.
  + *
  + * The [onError] function can take either the error object, or the error object
  + * and a stack as an argument. If [onError] was not provided, errors will get
  + * printed out to the stdout of this process.
  + */
   Future runAppEngine(AppEngineRequestHandler handler, {Function onError}) {
     var errorHandler;
     if (onError != null) {
  
positive.code:       try {
          request.response.statusCode = HttpStatus.INTERNAL_SERVER_ERROR;
        } on StateError catch (_) {}
        request.response.close().catchError((_) {
          errorHandler('Forcefully closing response, due to error in request '
                       'handler zone, resulted in an error: $error', stack);
        });
      });
    });
  
negative.code: /**
   * Returns the [ClientContext] of the current request.
   *
   * This getter can only be called inside a request handler which was passed to
   * [runAppEngine].
   */
  ClientContext get context {
    var context = Zone.current[_APPENGINE_CONTEXT];
  