[Sync] Add a sanity integration test for USS.

chrome/browser/sync/profile_sync_service_factory.cc

 // 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.
 
 #include "chrome/browser/sync/profile_sync_service_factory.h"
 
 #include <utility>
 
 #include "base/memory/ptr_util.h"
 #include "base/memory/singleton.h"
@@ skipping 152 matching lines @@
   // TODO(tim): Currently, AUTO/MANUAL settings refer to the *first* time sync
   // is set up and *not* a browser restart for a manual-start platform (where
   // sync has already been set up, and should be able to start without user
   // intervention). We can get rid of the browser_default eventually, but
   // need to take care that ProfileSyncService doesn't get tripped up between
   // those two cases. Bug 88109.
   init_params.start_behavior = browser_defaults::kSyncAutoStarts
                                    ? ProfileSyncService::AUTO_START
                                    : ProfileSyncService::MANUAL_START;
 
-  init_params.sync_client =
-      base::MakeUnique<browser_sync::ChromeSyncClient>(profile);
+  if (!client_factory_) {
+    init_params.sync_client =
+        base::MakeUnique<browser_sync::ChromeSyncClient>(profile);
+  } else {
+    init_params.sync_client = client_factory_->Run(profile);
+  }
 
   init_params.network_time_update_callback = base::Bind(&UpdateNetworkTime);
   init_params.base_directory = profile->GetPath();
   init_params.url_request_context = profile->GetRequestContext();
   init_params.debug_identifier = profile->GetDebugName();
   init_params.channel = chrome::GetChannel();
 
   init_params.db_thread = content::BrowserThread::GetTaskRunnerForThread(
       content::BrowserThread::DB);
   init_params.file_thread = content::BrowserThread::GetTaskRunnerForThread(
       content::BrowserThread::FILE);
   init_params.blocking_pool = content::BrowserThread::GetBlockingPool();
 
   auto pss = base::MakeUnique<ProfileSyncService>(std::move(init_params));
 
   // Will also initialize the sync client.
   pss->Initialize();
   return pss.release();
 }
 
 // static
 bool ProfileSyncServiceFactory::HasProfileSyncService(Profile* profile) {
   return GetInstance()->GetServiceForBrowserContext(profile, false) != NULL;
 }
+
+// static
+void ProfileSyncServiceFactory::SetSyncClientFactoryForTest(
+    SyncClientFactory* client_factory) {
+  client_factory_ = client_factory;
+}
+
+// static
+ProfileSyncServiceFactory::SyncClientFactory*
+    ProfileSyncServiceFactory::client_factory_ = nullptr;