fixes for angular hello: String + and disable broken arg parsing

lib/runtime/dart/async.js

 var async;
 (function(exports) {
   'use strict';
   // Function _invokeErrorHandler: (Function, Object, StackTrace) → dynamic
   function _invokeErrorHandler(errorHandler, error, stackTrace) {
     if (dart.is(errorHandler, ZoneBinaryCallback)) {
       return dart.dinvokef(errorHandler, error, stackTrace);
     } else {
       return dart.dinvokef(errorHandler, error);
     }
@@ skipping 25 matching lines @@
       if (stackTrace != null)
         return stackTrace;
       if (dart.is(error, core.Error)) {
         return dart.as(dart.dload(error, 'stackTrace'), core.StackTrace);
       }
       return null;
     }
     toString() {
       let result = `Uncaught Error: ${this.error}`;
       if (this.stackTrace != null) {
-        result = core.String['+'](result, `\nStack Trace:\n${this.stackTrace}`);
+        result = dart.notNull(result) + `\nStack Trace:\n${this.stackTrace}`;
       }
       return result;
     }
   }
   let _controller = Symbol('_controller');
   let _createSubscription = Symbol('_createSubscription');
   let _subscribe = Symbol('_subscribe');
   let _onListen = Symbol('_onListen');
   let _add = Symbol('_add');
   let _closeUnchecked = Symbol('_closeUnchecked');
@@ skipping 5139 matching lines @@
   exports.ScheduleMicrotaskHandler = ScheduleMicrotaskHandler;
   exports.CreateTimerHandler = CreateTimerHandler;
   exports.CreatePeriodicTimerHandler = CreatePeriodicTimerHandler;
   exports.PrintHandler = PrintHandler;
   exports.ForkHandler = ForkHandler;
   exports.ZoneSpecification = ZoneSpecification;
   exports.ZoneDelegate = ZoneDelegate;
   exports.Zone = Zone;
   exports.runZoned = runZoned;
 })(async || (async = {}));