[Sync] Refactoring of sync integration test checkers to remove boilerplate await methods.

chrome/browser/sync/test/integration/single_client_status_change_checker.cc

 // Copyright 2014 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/test/integration/single_client_status_change_checker.h"
 
 #include <vector>
 
 SingleClientStatusChangeChecker::SingleClientStatusChangeChecker(
     browser_sync::ProfileSyncService* service)
-    : MultiClientStatusChangeChecker(
-          std::vector<browser_sync::ProfileSyncService*>(1, service)) {}
+    : MultiClientStatusChangeChecker({service}) {}
 
 SingleClientStatusChangeChecker::~SingleClientStatusChangeChecker() {}
 
 browser_sync::ProfileSyncService* SingleClientStatusChangeChecker::service() {
   return services()[0];
 }