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

content/browser/appcache/appcache_subresource_url_factory.h

Index: content/browser/appcache/appcache_subresource_url_factory.h
diff --git a/content/browser/appcache/appcache_subresource_url_factory.h b/content/browser/appcache/appcache_subresource_url_factory.h
index ef4458e8a5129e50d466a159830a27228e0261bf..40f36a9363fa5c528aa737a4128108e2c6dbf2f7 100644
--- a/content/browser/appcache/appcache_subresource_url_factory.h
+++ b/content/browser/appcache/appcache_subresource_url_factory.h
@@ -7,6 +7,7 @@
 
 #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"
@@ -20,7 +21,8 @@ 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;
 
@@ -53,12 +55,23 @@ class AppCacheSubresourceURLFactory : public mojom::URLLoaderFactory {
                 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_;