feat(di): Add the @Injectable annotation to Compiler

Mark `Compiler` and its dependencies as available to the `Injector`.

modules/angular2/src/core/compiler/xhr/xhr_impl.dart

@@ -1,7 +1,9 @@
 import 'dart:async';
 import 'dart:html';
+import 'package:angular2/di.dart';
 import './xhr.dart' show XHR;
 
+@Injectable()
 class XHRImpl extends XHR {
   Future<String> get(String url) {
     return HttpRequest.request(url).then(

modules/angular2/src/core/compiler/xhr/xhr_impl.es6

@@ -1,6 +1,8 @@
+import {Injectable} from 'angular2/di';
 import {Promise, PromiseWrapper} from 'angular2/src/facade/async';
 import {XHR} from './xhr';
 
+@Injectable()
 export class XHRImpl extends XHR {
   get(url: string): Promise<string> {
     var completer = PromiseWrapper.completer();