feat(testability): hook zone into whenstable api with async support

closes(#428)

modules/examples/e2e_test/async/async_spec.ts

@@ -0,0 +1,71 @@
+import {verifyNoBrowserErrors} from 'angular2/src/test_lib/e2e_util';
+
+function whenStable(rootSelector) {
+  // TODO(hankduan): remove this call once Protractor implements it
+  return browser.executeAsyncScript('var el = document.querySelector("' + rootSelector + '");' +
+                                    'window.getAngularTestability(el).whenStable(arguments[0]);');
+};
+
+describe('async', () => {
+  var URL = 'examples/src/async/index.html';
+
+  beforeEach(() => browser.get(URL));
+
+  it('should work with synchronous actions', () => {
+    var increment = $('#increment');
+    increment.$('.action').click();
+
+    expect(increment.$('.val').getText()).toEqual('1');
+  });
+
+  it('should wait for asynchronous actions', () => {
+    var timeout = $('#delayedIncrement');
+    timeout.$('.action').click();
+
+    // At this point, the async action is still pending, so the count should
+    // still be 0.
+    expect(timeout.$('.val').getText()).toEqual('0');
+
+    whenStable('async-app')
+        .then(() => {
+          // whenStable should only be called when the async action finished,
+          // so the count should be 1 at this point.
+          expect(timeout.$('.val').getText()).toEqual('1');
+        });
+  });
+
+  it('should notice when asynchronous actions are cancelled', () => {
+    var timeout = $('#delayedIncrement');
+    timeout.$('.action').click();
+
+    // At this point, the async action is still pending, so the count should
+    // still be 0.
+    expect(timeout.$('.val').getText()).toEqual('0');
+
+    timeout.$('.cancel').click();
+    whenStable('async-app')
+        .then(() => {
+          // whenStable should be called since the async action is cancelled. The
+          // count should still be 0;
+          expect(timeout.$('.val').getText()).toEqual('0');
+        });
+  });
+
+  it('should wait for a series of asynchronous actions', () => {
+    var timeout = $('#multiDelayedIncrements');
+    timeout.$('.action').click();
+
+    // At this point, the async action is still pending, so the count should
+    // still be 0.
+    expect(timeout.$('.val').getText()).toEqual('0');
+
+    whenStable('async-app')
+        .then(() => {
+          // whenStable should only be called when all the async actions
+          // finished, so the count should be 10 at this point.
+          expect(timeout.$('.val').getText()).toEqual('10');
+        });
+  });
+
+  afterEach(verifyNoBrowserErrors);
+});