feat(compiler): Add an implementation for XHR that uses a template cache to load template files.

Useful for avoiding doing an actual XHR during testing.
Part of the solution for #4051 (Other part is a Karma plugin that will create the template cache).

Closes #7940

modules/angular2/src/platform/browser/xhr_cache.dart

@@ -0,0 +1,48 @@
+library angular2.src.services.xhr_cache;
+
+import 'dart:async' show Future;
+import 'dart:html';
+import 'dart:js' as js;
+import 'package:angular2/core.dart';
+import 'package:angular2/src/compiler/xhr.dart';
+import 'package:angular2/src/facade/exceptions.dart' show BaseException;
+
+/**
+ * An implementation of XHR that uses a template cache to avoid doing an actual
+ * XHR.
+ *
+ * The template cache needs to be built and loaded into window.$templateCache
+ * via a separate mechanism.
+ */
+@Injectable()
+class CachedXHR extends XHR {
+  js.JsObject _cache;
+  String _baseUri;
+
+  CachedXHR() {
+    if (js.context.hasProperty(r'$templateCache')) {
+      this._cache = js.context[r'$templateCache'];
+    } else {
+      throw new BaseException(
+        r'CachedXHR: Template cache was not found in $templateCache.');
+    }
+    this._baseUri = window.location.protocol +
+      '//' +
+      window.location.host +
+      window.location.pathname;
+    int lastSlash = this._baseUri.lastIndexOf('/');
+    this._baseUri = this._baseUri.substring(0, lastSlash + 1);
+  }
+
+  Future<String> get(String url) {
+    if (url.startsWith(this._baseUri)) {
+      url = url.substring(this._baseUri.length);
+    }
+    if (this._cache.hasProperty(url)) {
+      return new Future.value(this._cache[url]);
+    } else {
+      return new Future.error(
+        'CachedXHR: Did not find cached template for ' + url);
+    }
+  }
+}

modules/angular2/src/platform/browser/xhr_cache.ts

@@ -0,0 +1,31 @@
+import {XHR} from 'angular2/src/compiler/xhr';
+import {BaseException} from 'angular2/src/facade/exceptions';
+import {global} from 'angular2/src/facade/lang';
+import {PromiseWrapper} from 'angular2/src/facade/promise';
+
+/**
+ * An implementation of XHR that uses a template cache to avoid doing an actual
+ * XHR.
+ *
+ * The template cache needs to be built and loaded into window.$templateCache
+ * via a separate mechanism.
+ */
+export class CachedXHR extends XHR {
+  private _cache: {[url: string]: string};
+
+  constructor() {
+    super();
+    this._cache = (<any>global).$templateCache;
+    if (this._cache == null) {
+      throw new BaseException('CachedXHR: Template cache was not found in $templateCache.');
+    }
+  }
+
+  get(url: string): Promise<string> {
+    if (this._cache.hasOwnProperty(url)) {
+      return PromiseWrapper.resolve(this._cache[url]);
+    } else {
+      return PromiseWrapper.reject('CachedXHR: Did not find cached template for ' + url, null);
+    }
+  }
+}

modules/angular2/src/platform/browser_common.ts

@@ -1,6 +1,6 @@
 import {CONST_EXPR, IS_DART} from 'angular2/src/facade/lang';
 import {provide, Provider, Injector, OpaqueToken} from 'angular2/src/core/di';
-
+import {XHR} from 'angular2/src/compiler/xhr';
 import {
   PLATFORM_INITIALIZER,
   PLATFORM_DIRECTIVES,
@@ -28,6 +28,7 @@ import {BrowserDetails} from "angular2/src/animate/browser_details";
 import {AnimationBuilder} from "angular2/src/animate/animation_builder";
 import {BrowserDomAdapter} from './browser/browser_adapter';
 import {BrowserGetTestability} from 'angular2/src/platform/browser/testability';
+import {CachedXHR} from 'angular2/src/platform/browser/xhr_cache';
 import {wtfInit} from 'angular2/src/core/profile/wtf_init';
 import {EventManager, EVENT_MANAGER_PLUGINS} from "angular2/src/platform/dom/events/event_manager";
 import {
@@ -94,6 +95,9 @@ export const BROWSER_APP_COMMON_PROVIDERS: Array<any /*Type | Provider | any[]*/
   ELEMENT_PROBE_PROVIDERS
 ]);
 
+export const CACHED_TEMPLATE_PROVIDER: Array<any /*Type | Provider | any[]*/> =
+    CONST_EXPR([new Provider(XHR, {useClass: CachedXHR})]);
+
 export function initDomAdapter() {
   BrowserDomAdapter.makeCurrent();
   wtfInit();