fix(WebWorker): Add zone support to MessageBus

Closes #4053

modules/angular2/src/mock/ng_zone_mock.ts

@@ -1,9 +1,17 @@
 import {NgZone} from 'angular2/src/core/zone/ng_zone';
 
 export class MockNgZone extends NgZone {
+  _onEventDone: () => void;
+
   constructor() { super({enableLongStackTrace: false}); }
 
   run(fn: Function): any { return fn(); }
 
   runOutsideAngular(fn: Function): any { return fn(); }
+
+  overrideOnEventDone(fn: () => void, opt_waitForAsync: boolean = false): void {
+    this._onEventDone = fn;
+  }
+
+  simulateZoneExit(): void { this._onEventDone(); }
 }