feat(common): new HttpClient API

HttpClient is an evolution of the existing Angular HTTP API, which exists
alongside of it in a separate package, @angular/common/http. This structure
ensures that existing codebases can slowly migrate to the new API.

The new API improves significantly on the ergonomics and features of the legacy
API. A partial list of new features includes:

* Typed, synchronous response body access, including support for JSON body types
* JSON is an assumed default and no longer needs to be explicitly parsed
* Interceptors allow middleware logic to be inserted into the pipeline
* Immutable request/response objects
* Progress events for both request upload and response download
* Post-request verification & flush based testing framework

packages/common/http/testing/src/module.ts

@@ -0,0 +1,34 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {HttpBackend, HttpClientModule} from '@angular/common/http';
+import {NgModule} from '@angular/core';
+
+import {HttpTestingController} from './api';
+import {HttpClientTestingBackend} from './backend';
+
+
+/**
+ * Configures `HttpClientTestingBackend` as the `HttpBackend` used by `HttpClient`.
+ *
+ * Inject `HttpTestingController` to expect and flush requests in your tests.
+ *
+ * @experimental
+ */
+@NgModule({
+  imports: [
+    HttpClientModule,
+  ],
+  providers: [
+    HttpClientTestingBackend,
+    {provide: HttpBackend, useExisting: HttpClientTestingBackend},
+    {provide: HttpTestingController, useExisting: HttpClientTestingBackend},
+  ],
+})
+export class HttpClientTestingModule {
+}