fix(services): export title service

Signed-off-by: cexbrayat <cedric@ninja-squad.com>

Closes #4271

modules/angular2/src/core/services.ts

@@ -1,3 +1,4 @@
 // Public API for Services
 export {AppRootUrl} from 'angular2/src/core/services/app_root_url';
 export {UrlResolver} from 'angular2/src/core/services/url_resolver';
+export {Title} from 'angular2/src/core/services/title';

modules/angular2/test/public_api_spec.ts

@@ -973,6 +973,9 @@ var NG_API = [
   'TemplateRef.hasLocal()',
   'TemplateRef.protoViewRef',
   'Type:js',
+  'Title',
+  'Title.getTitle()',
+  'Title.setTitle()',
   'TypeLiteral',
   'TypeLiteral.type',
   'UpperCasePipe',