Register factories for ExternalProviderImplChromeOSTest

When using IdentityTestEnvironmentProfileAdaptor, it is required
to register the testing factories when creating the Profile, as
the adaptor will expect the IdentityManager to have been created
with certain fakes.

If the factories are not set, then it is possible to encounter
Undefined Behaviour (as IdentityTestEnvironment cast some of the
objects to the expected fake subclasses) in the worst case or
just non-fonctioning test (calling undefined methods) on certain
platforms.

Fix ExternalProviderImplChromeOSTest to use the proper factory
by registering them in the super class.

Bug: 982751
Change-Id: Id116ee5b0df4b69ccf31a152c3c0318aaf94ef45
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1809158
Auto-Submit: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Finnur Thorarinsson <finnur@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697571}

chrome/browser/extensions/extension_service_test_base.cc

@@ -24,6 +24,8 @@
 #include "chrome/browser/extensions/test_extension_system.h"
 #include "chrome/browser/extensions/updater/extension_updater.h"
 #include "chrome/browser/prefs/browser_prefs.h"
+#include "chrome/browser/signin/identity_manager_factory.h"
+#include "chrome/browser/signin/identity_test_environment_profile_adaptor.h"
 #include "chrome/common/chrome_constants.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/test/base/testing_browser_process.h"
@@ -69,6 +71,10 @@ std::unique_ptr<TestingProfile> BuildTestingProfile(
   if (params.profile_is_supervised)
     profile_builder.SetSupervisedUserId("asdf");
 
+  profile_builder.AddTestingFactories(
+      IdentityTestEnvironmentProfileAdaptor::
+          GetIdentityTestEnvironmentFactories());
+
   profile_builder.SetPath(params.profile_path);
   return profile_builder.Build();
 }