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

google_apis/gcm/monitoring/gcm_stats_recorder.h

Index: google_apis/gcm/monitoring/gcm_stats_recorder.h
diff --git a/google_apis/gcm/monitoring/gcm_stats_recorder.h b/google_apis/gcm/monitoring/gcm_stats_recorder.h
index 8a093ebbb8232556118c15e3215cfb36651b29fa..72c4446e26d0730116624da4e640f7ea9cce6ce7 100644
--- a/google_apis/gcm/monitoring/gcm_stats_recorder.h
+++ b/google_apis/gcm/monitoring/gcm_stats_recorder.h
@@ -52,7 +52,8 @@ class GCM_EXPORT GCMStatsRecorder {
 
   // Records that a check-in request has failed. If a retry will be tempted then
   // will_retry should be true.
-  virtual void RecordCheckinFailure(std::string status, bool will_retry) = 0;
+  virtual void RecordCheckinFailure(const std::string& status,
+                                    bool will_retry) = 0;
 
   // Records that a connection to MCS has been initiated.
   virtual void RecordConnectionInitiated(const std::string& host) = 0;