Change AuthenticatingURLLoader to be a URLLoaderInterceptor

This CL changes AuthenticatingURLLoader to be a URLLoaderInterceptor rather
than a one-off interface whose implementation wrapped URLLoaders. Renaming of
various classes/files to more appropriate names will happen in a follow-up CL
to minimize churn.

It also removes the background loader used to load the
authenticating_url_loader app; it is no longer needed as the NetworkService's
URLLoaders are now being used directly again and can fetch the
authenticating_url_loader app.

R=qsr@chromium.org

Review URL: https://codereview.chromium.org/1155283003
diff --git a/shell/application_manager/application_manager.h b/shell/application_manager/application_manager.h
index 23cde5e..12a0c7b 100644
--- a/shell/application_manager/application_manager.h
+++ b/shell/application_manager/application_manager.h
@@ -14,7 +14,7 @@
 #include "mojo/public/cpp/bindings/interface_request.h"
 #include "mojo/public/interfaces/application/application.mojom.h"
 #include "mojo/public/interfaces/application/service_provider.mojom.h"
-#include "mojo/services/authenticating_url_loader/public/interfaces/authenticating_url_loader_factory.mojom.h"
+#include "mojo/services/network/public/interfaces/network_service.mojom.h"
 #include "mojo/services/url_response_disk_cache/public/interfaces/url_response_disk_cache.mojom.h"
 #include "shell/application_manager/application_loader.h"
 #include "shell/application_manager/identity.h"
@@ -240,10 +240,10 @@
 
   base::SequencedWorkerPool* blocking_pool_;
   mojo::URLResponseDiskCachePtr url_response_disk_cache_;
-  mojo::AuthenticatingURLLoaderFactoryPtr url_loader_factory_;
+  mojo::NetworkServicePtr network_service_;
   MimeTypeToURLMap mime_type_to_url_;
   ScopedVector<NativeRunner> native_runners_;
-  bool initialized_authentication_service_;
+  bool initialized_authentication_interceptor_;
   base::WeakPtrFactory<ApplicationManager> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ApplicationManager);