[Sync] Add a sanity integration test for USS.

chrome/browser/sync/profile_sync_service_factory.h

 // Copyright (c) 2012 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 CHROME_BROWSER_SYNC_PROFILE_SYNC_SERVICE_FACTORY_H_
 #define CHROME_BROWSER_SYNC_PROFILE_SYNC_SERVICE_FACTORY_H_
 
 #include "base/macros.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 
 namespace base {
 template <typename T>
 struct DefaultSingletonTraits;
 }
 
 namespace sync_driver {
+class SyncClient;
 class SyncService;
 }
 
 class Profile;
 class ProfileSyncService;
 
 class ProfileSyncServiceFactory : public BrowserContextKeyedServiceFactory {
  public:
+  typedef base::Callback<std::unique_ptr<sync_driver::SyncClient>(Profile*)>
+      SyncClientFactory;
+
   static ProfileSyncService* GetForProfile(Profile* profile);
   static bool HasProfileSyncService(Profile* profile);
 
   // Convenience method that returns the ProfileSyncService as a
   // sync_driver::SyncService.
   static sync_driver::SyncService* GetSyncServiceForBrowserContext(
       content::BrowserContext* context);
 
   static ProfileSyncServiceFactory* GetInstance();
 
+  // Overrides how the SyncClient is created for testing purposes.
+  static void SetSyncClientFactoryForTest(SyncClientFactory* client_factory);
+
  private:
   friend struct base::DefaultSingletonTraits<ProfileSyncServiceFactory>;
 
   ProfileSyncServiceFactory();
   ~ProfileSyncServiceFactory() override;
 
   // BrowserContextKeyedServiceFactory:
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* context) const override;
 
+  // A factory function for overriding the way the SyncClient is created.
+  // This is a raw pointer so it can be statically initialized.
+  static SyncClientFactory* client_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(ProfileSyncServiceFactory);
 };
 
 #endif  // CHROME_BROWSER_SYNC_PROFILE_SYNC_SERVICE_FACTORY_H_