[Sync] Add a sanity integration test for USS.

chrome/browser/sync/profile_sync_service_factory.h

Index: chrome/browser/sync/profile_sync_service_factory.h
diff --git a/chrome/browser/sync/profile_sync_service_factory.h b/chrome/browser/sync/profile_sync_service_factory.h
index 31d0c4d07e8c3d31cc90175b9fe644da369adbbc..4c8c6c9e30238dbd69f69c3611a8b733a18e11f2 100644
--- a/chrome/browser/sync/profile_sync_service_factory.h
+++ b/chrome/browser/sync/profile_sync_service_factory.h
@@ -14,6 +14,7 @@ struct DefaultSingletonTraits;
 }
 
 namespace sync_driver {
+class SyncClient;
 class SyncService;
 }
 
@@ -22,6 +23,9 @@ 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);
 
@@ -32,6 +36,9 @@ class ProfileSyncServiceFactory : public BrowserContextKeyedServiceFactory {
 
   static ProfileSyncServiceFactory* GetInstance();
 
+  // Overrides how the SyncClient is created for testing purposes.
+  static void SetSyncClientFactoryForTest(SyncClientFactory* client_factory);
+
  private:
   friend struct base::DefaultSingletonTraits<ProfileSyncServiceFactory>;
 
@@ -42,6 +49,10 @@ class ProfileSyncServiceFactory : public 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);
 };