The Appcache subresource URL factory needs to inform the URLLoaderClient if there is a failure.

content/browser/appcache/appcache_subresource_url_factory.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_APPCACHE_APPCACHE_SUBRESOURCE_URL_FACTORY_H_
 #define CONTENT_BROWSER_APPCACHE_APPCACHE_SUBRESOURCE_URL_FACTORY_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
+#include "content/common/content_export.h"
 #include "content/public/common/url_loader_factory.mojom.h"
 #include "mojo/public/cpp/bindings/binding.h"
 #include "net/traffic_annotation/network_traffic_annotation.h"
 #include "url/gurl.h"
 
 namespace content {
 
 class AppCacheHost;
 class AppCacheJob;
 class AppCacheServiceImpl;
 class URLLoaderFactoryGetter;
 
 // Implements the URLLoaderFactory mojom for AppCache subresource requests.
-class AppCacheSubresourceURLFactory : public mojom::URLLoaderFactory {
+class CONTENT_EXPORT AppCacheSubresourceURLFactory
+    : public mojom::URLLoaderFactory {
  public:
   ~AppCacheSubresourceURLFactory() override;
 
   // Factory function to create an instance of the factory.
   // 1. The |factory_getter| parameter is used to query the network service
   //    to pass network requests to.
   // 2. The |host| parameter contains the appcache host instance. This is used
   //    to create the AppCacheRequestHandler instances for handling subresource
   //    requests.
   // Returns the AppCacheSubresourceURLFactory instance. The URLLoaderFactoryPtr
@@ skipping 12 matching lines @@
       const ResourceRequest& request,
       mojom::URLLoaderClientPtr client,
       const net::MutableNetworkTrafficAnnotationTag& traffic_annotation)
       override;
   void SyncLoad(int32_t routing_id,
                 int32_t request_id,
                 const ResourceRequest& request,
                 SyncLoadCallback callback) override;
 
  private:
+  friend class AppCacheNetworkServiceBrowserTest;
+
   AppCacheSubresourceURLFactory(mojom::URLLoaderFactoryRequest request,
                                 URLLoaderFactoryGetter* factory_getter,
                                 base::WeakPtr<AppCacheHost> host);
 
   void OnConnectionError();
 
+  // Notifies the |client| if there is a failure. The |error_code| contains the
+  // actual error.
+  void NotifyError(mojom::URLLoaderClientPtr client, int error_code);
+
+  // Passes a flag |for_testing| indicating that we are in test mode. Certain
+  // behaviors like returning errors for a missing host, etc are turned off in

[jam, 2017/07/25 15:00:51]

this seems specific to this one test; it's not intuitive what 'testing mode'
causes to fail, and a boolean won't scale for other tests that want different
behavior.

is there another way we can do this without changing the production code? what
if the test sets up a C++ handler for the EmbeddedTestServer using
RegisterRequestHandler (example:
https://cs.chromium.org/chromium/src/net/test/embedded_test_server/embedded_t...).
Then it can count how many times chrome goes to the network. If the old
(appcache) subresource loader is used, then we'd have fewer server hits than we
expect.

[ananta, 2017/07/25 22:26:49]

Thanks. done. I had to create a custom embedded server to ensure that the
handler gets added at the front of the other handlers. The base class also
creates a server. However it registers the default handlers before  us which
causes our handler to never get called.

+  // this mode. Defaults to false.
+  static void SetForTesting(bool for_testing);
+
   // Mojo binding.
   mojo::Binding<mojom::URLLoaderFactory> binding_;
 
   // Used to retrieve the network service factory to pass unhandled requests to
   // the network service.
   scoped_refptr<URLLoaderFactoryGetter> default_url_loader_factory_getter_;
 
   base::WeakPtr<AppCacheHost> appcache_host_;
 
   DISALLOW_COPY_AND_ASSIGN(AppCacheSubresourceURLFactory);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_APPCACHE_APPCACHE_URL_LOADER_FACTORY_H_