Convert Pass()→std::move() for iOS build.

ios/chrome/browser/signin/account_tracker_service_factory.cc

 // Copyright 2015 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 "ios/chrome/browser/signin/account_tracker_service_factory.h"
 
+#include <utility>
+
 #include "base/memory/singleton.h"
 #include "components/keyed_service/ios/browser_state_dependency_manager.h"
 #include "components/signin/core/browser/account_tracker_service.h"
 #include "ios/chrome/browser/signin/signin_client_factory.h"
 #include "ios/public/provider/chrome/browser/browser_state/chrome_browser_state.h"
 
 namespace ios {
 
 AccountTrackerServiceFactory::AccountTrackerServiceFactory()
     : BrowserStateKeyedServiceFactory(
@@ skipping 21 matching lines @@
   AccountTrackerService::RegisterPrefs(registry);
 }
 
 scoped_ptr<KeyedService> AccountTrackerServiceFactory::BuildServiceInstanceFor(
     web::BrowserState* context) const {
   ios::ChromeBrowserState* chrome_browser_state =
       ios::ChromeBrowserState::FromBrowserState(context);
   scoped_ptr<AccountTrackerService> service(new AccountTrackerService());
   service->Initialize(
       SigninClientFactory::GetForBrowserState(chrome_browser_state));
-  return service.Pass();
+  return std::move(service);
 }
 
 }  // namespace ios