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/test/public_api_spec.ts

@@ -288,6 +288,7 @@ var NG_PLATFORM_BROWSER = [
   'BROWSER_PROVIDERS',
   'BrowserDomAdapter',
   'By',
+  'CACHED_TEMPLATE_PROVIDER',
   'DOCUMENT',
   'ELEMENT_PROBE_PROVIDERS',
   'ELEMENT_PROBE_PROVIDERS_PROD_MODE',