feat: introduce Title service

Closes #612

Closes #900

modules/angular2/test/services/title_spec.js

@@ -0,0 +1,32 @@
+import {ddescribe, describe, it, iit, xit, expect, afterEach} from 'angular2/test_lib';
+import {DOM} from 'angular2/src/dom/dom_adapter';
+
+import {Title} from 'angular2/src/services/title';
+
+export function main() {
+
+  describe('title service', () => {
+    var initialTitle = DOM.getTitle();
+    var titleService = new Title();
+
+    afterEach(() => {
+      DOM.setTitle(initialTitle);
+    });
+
+    it('should allow reading initial title', () => {
+      expect(titleService.getTitle()).toEqual(initialTitle);
+    });
+
+    it('should set a title on the injected document', () => {
+      titleService.setTitle('test title');
+      expect(DOM.getTitle()).toEqual('test title');
+      expect(titleService.getTitle()).toEqual('test title');
+    });
+
+    it('should reset title to empty string if title not provided', () => {
+      titleService.setTitle(null);
+      expect(DOM.getTitle()).toEqual('');
+    });
+
+  });
+}