fix(WebWorkers): Run XHR requests on the UI

Fixes issues in dart where dart:html is not available in isolates and
allows for better profiling of XHR requests

Closes #3652

modules/angular2/test/web-workers/worker/renderer_spec.ts

@@ -55,7 +55,7 @@ export function main() {
 
     // set up the ui side
     var webWorkerMain = new WebWorkerMain(tb.compiler, tb.renderer, uiRenderViewStore, uiSerializer,
-                                          new AnchorBasedAppRootUrl());
+                                          new AnchorBasedAppRootUrl(), null);
     webWorkerMain.attachToWebWorker(uiMessageBus);
     return broker;
   }

modules/angular2/test/web-workers/worker/xhr_impl_spec.ts

@@ -0,0 +1,49 @@
+import {
+  AsyncTestCompleter,
+  inject,
+  describe,
+  it,
+  expect,
+  beforeEach,
+  createTestInjector,
+  beforeEachBindings,
+  SpyObject,
+  proxy
+} from 'angular2/test_lib';
+import {IMPLEMENTS, Type} from 'angular2/src/facade/lang';
+import {MessageBroker, UiArguments} from 'angular2/src/web-workers/worker/broker';
+import {WebWorkerXHRImpl} from "angular2/src/web-workers/worker/xhr_impl";
+import {PromiseWrapper} from "angular2/src/facade/async";
+
+export function main() {
+  describe("WebWorkerXHRImpl", () => {
+    it("should pass requests through the broker and return the response",
+       inject([AsyncTestCompleter], (async) => {
+         const URL = "http://www.example.com/test";
+         const RESPONSE = "Example response text";
+
+         var messageBroker: any = new SpyMessageBroker();
+         messageBroker.spy("runOnUiThread")
+             .andCallFake((args: UiArguments, returnType: Type) => {
+               expect(args.type).toEqual("xhr");
+               expect(args.method).toEqual("get");
+               expect(args.args.length).toEqual(1);
+               expect(args.args[0].value).toEqual(URL);
+               return PromiseWrapper.wrap(() => { return RESPONSE; });
+             });
+
+         var xhrImpl = new WebWorkerXHRImpl(messageBroker);
+         xhrImpl.get(URL).then((response) => {
+           expect(response).toEqual(RESPONSE);
+           async.done();
+         });
+       }));
+  });
+}
+
+@proxy
+@IMPLEMENTS(MessageBroker)
+class SpyMessageBroker extends SpyObject {
+  constructor() { super(MessageBroker); }
+  noSuchMethod(m) { return super.noSuchMethod(m); }
+}