fix(router): respond to hashchange events

Previously if the URL changed in `HashLocation` mode, the router would not pick up the change.
This adds a listener in `HashLocationStrategy` for `hashchange` events to fix the problem.

Closes #5013

modules/playground/e2e_test/hash_routing/hash_location_spec.dart

@@ -0,0 +1,3 @@
+library playground.e2e_test.hash_location_spec;
+
+main() {}

modules/playground/e2e_test/hash_routing/hash_location_spec.ts

@@ -0,0 +1,29 @@
+import {verifyNoBrowserErrors} from 'angular2/src/testing/e2e_util';
+import {Promise} from 'angular2/src/core/facade/async';
+
+function waitForElement(selector) {
+  var EC = (<any>protractor).ExpectedConditions;
+  // Waits for the element with id 'abc' to be present on the dom.
+  browser.wait(EC.presenceOf($(selector)), 20000);
+}
+
+describe('hash routing example app', function() {
+  afterEach(verifyNoBrowserErrors);
+
+  var URL = 'playground/src/hash_routing/index.html';
+
+  it('should navigate between routes', function() {
+    browser.get(URL + '#/bye');
+    waitForElement('goodbye-cmp');
+
+    element(by.css('#hello-link')).click();
+    waitForElement('hello-cmp');
+
+    expect(element(by.css('hello-cmp')).getText()).toContain('hello');
+
+    browser.navigate().back();
+    waitForElement('goodbye-cmp');
+
+    expect(element(by.css('goodbye-cmp')).getText()).toContain('goodbye');
+  });
+});