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

components/gcm_driver/gcm_stats_recorder_impl.h

Index: components/gcm_driver/gcm_stats_recorder_impl.h
diff --git a/components/gcm_driver/gcm_stats_recorder_impl.h b/components/gcm_driver/gcm_stats_recorder_impl.h
index de11d49121b0d84ae4c6746caec45af3e76c4f82..1656bb8536bfaceb762fc4db084ff7bb0ae22ff5 100644
--- a/components/gcm_driver/gcm_stats_recorder_impl.h
+++ b/components/gcm_driver/gcm_stats_recorder_impl.h
@@ -47,7 +47,8 @@ class GCMStatsRecorderImpl : public GCMStatsRecorder {
   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;