Cleanup: Pass std::string as const reference if possible

components/gcm_driver/gcm_stats_recorder_impl.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 COMPONENTS_GCM_DRIVER_GCM_STATS_RECORDER_IMPL_H_
 #define COMPONENTS_GCM_DRIVER_GCM_STATS_RECORDER_IMPL_H_
 
 #include <deque>
 #include <string>
 #include <vector>
@@ skipping 29 matching lines @@
   // Set a delegate to receive callback from the recorder.
   void SetDelegate(Delegate* delegate);
 
   // Clear all recorded activities.
   void Clear();
 
   // GCMStatsRecorder implementation:
   void RecordCheckinInitiated(uint64 android_id) override;
   void RecordCheckinDelayedDueToBackoff(int64 delay_msec) override;
   void RecordCheckinSuccess() override;
-  void RecordCheckinFailure(std::string status, bool will_retry) override;
+  void RecordCheckinFailure(const std::string& status,
+                            bool will_retry) override;
   void RecordConnectionInitiated(const std::string& host) override;
   void RecordConnectionDelayedDueToBackoff(int64 delay_msec) override;
   void RecordConnectionSuccess() override;
   void RecordConnectionFailure(int network_error) override;
   void RecordConnectionResetSignaled(
       ConnectionFactory::ConnectionResetReason reason) override;
   void RecordRegistrationSent(const std::string& app_id,
                               const std::string& source) override;
   void RecordRegistrationResponse(const std::string& app_id,
                                   const std::string& source,
@@ skipping 94 matching lines @@
   base::TimeTicks last_received_data_message_burst_start_time_;
   base::TimeTicks last_received_data_message_time_within_burst_;
   int64 received_data_message_burst_size_;
 
   DISALLOW_COPY_AND_ASSIGN(GCMStatsRecorderImpl);
 };
 
 }  // namespace gcm
 
 #endif  // COMPONENTS_GCM_DRIVER_GCM_STATS_RECORDER_IMPL_H_