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,