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/platform/browser.ts

@@ -1,6 +1,7 @@
 export {AngularEntrypoint} from 'angular2/src/core/angular_entrypoint';
 export {
   BROWSER_PROVIDERS,
+  CACHED_TEMPLATE_PROVIDER,
   ELEMENT_PROBE_PROVIDERS,
   ELEMENT_PROBE_PROVIDERS_PROD_MODE,
   inspectNativeElement,

modules/angular2/platform/testing/browser.ts

@@ -2,12 +2,15 @@ import {
   TEST_BROWSER_STATIC_PLATFORM_PROVIDERS,
   ADDITIONAL_TEST_BROWSER_PROVIDERS
 } from 'angular2/platform/testing/browser_static';
-
 import {BROWSER_APP_PROVIDERS} from 'angular2/platform/browser';
-
-
 import {CONST_EXPR} from 'angular2/src/facade/lang';
 
+/**
+ * Providers for using template cache to avoid actual XHR.
+ * Re-exported here so that tests import from a single place.
+ */
+export {CACHED_TEMPLATE_PROVIDER} from 'angular2/platform/browser';
+
 /**
  * Default patform providers for testing.
  */