feat(compiler, ShadowDom): adds TemplateLoader using XHR.

Also adds css shimming for emulated shadow dom and makes the shadowDom
strategy global to the application.

modules/angular2/src/core/compiler/xhr/xhr.js

@@ -0,0 +1,7 @@
+import {Promise} from 'angular2/src/facade/async';
+
+export class XHR {
+  get(url: string): Promise<string> {
+    return null;
+  }
+}

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

@@ -0,0 +1,12 @@
+import 'dart:async';
+import 'dart:html';
+import './xhr.dart' show XHR;
+
+class XHRImpl extends XHR {
+  Future<String> get(String url) {
+    return HttpRequest.request(url).then(
+      (HttpRequest request) => request.responseText,
+      onError: (Error e) => throw 'Failed to load $url'
+    );
+  }
+}

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

@@ -0,0 +1,27 @@
+import {Promise, PromiseWrapper} from 'angular2/src/facade/async';
+import {XHR} from './xhr';
+
+export class XHRImpl extends XHR {
+  get(url: string): Promise<string> {
+    var completer = PromiseWrapper.completer();
+    var xhr = new XMLHttpRequest();
+    xhr.open('GET', url, true);
+    xhr.responseType = 'text';
+
+    xhr.onload = function() {
+      var status = xhr.status;
+      if (200 <= status && status <= 300) {
+        completer.complete(xhr.responseText);
+      } else {
+        completer.reject(`Failed to load ${url}`);
+      }
+    };
+
+    xhr.onerror = function() {
+      completer.reject(`Failed to load ${url}`);
+    };
+
+    xhr.send();
+    return completer.promise;
+  }
+}