[Sync] Fixing easy lint violations.

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

 // 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.
 
 #ifndef CHROME_BROWSER_SYNC_TEST_INTEGRATION_SINGLE_CLIENT_STATUS_CHANGE_CHECKER_H_
 #define CHROME_BROWSER_SYNC_TEST_INTEGRATION_SINGLE_CLIENT_STATUS_CHANGE_CHECKER_H_
 
+#include <string>
+
 #include "base/compiler_specific.h"
 #include "base/time/time.h"
 #include "chrome/browser/sync/test/integration/multi_client_status_change_checker.h"
 #include "components/sync/driver/sync_service_observer.h"
 
 namespace browser_sync {
 class ProfileSyncService;
 }  // namespace browser_sync
 
 // This class provides some common functionality for StatusChangeCheckers that
 // observe only one ProfileSyncService.  This class is abstract.  Its
 // descendants are expected to provide additional functionality.
 class SingleClientStatusChangeChecker
   : public MultiClientStatusChangeChecker {
  public:
   explicit SingleClientStatusChangeChecker(
       browser_sync::ProfileSyncService* service);
   ~SingleClientStatusChangeChecker() override;
 
   // StatusChangeChecker implementations and stubs.
   bool IsExitConditionSatisfied() override = 0;
   std::string GetDebugMessage() const override = 0;
 
  protected:
   browser_sync::ProfileSyncService* service();
 };
 
 #endif  // CHROME_BROWSER_SYNC_TEST_INTEGRATION_SINGLE_CLIENT_STATUS_CHANGE_CHECKER_H_