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

components/gcm_driver/gcm_stats_recorder_impl.cc

Index: components/gcm_driver/gcm_stats_recorder_impl.cc
diff --git a/components/gcm_driver/gcm_stats_recorder_impl.cc b/components/gcm_driver/gcm_stats_recorder_impl.cc
index 1e40fb58a7ea90c98f9fbcfe13e37dd86f54a666..e1731c707602ff7b9bdc57846152dfe83f9edb5a 100644
--- a/components/gcm_driver/gcm_stats_recorder_impl.cc
+++ b/components/gcm_driver/gcm_stats_recorder_impl.cc
@@ -206,8 +206,8 @@ void GCMStatsRecorderImpl::RecordCheckinSuccess() {
   RecordCheckin("Checkin succeeded", std::string());
 }
 
-void GCMStatsRecorderImpl::RecordCheckinFailure(std::string status,
-                                            bool will_retry) {
+void GCMStatsRecorderImpl::RecordCheckinFailure(const std::string& status,
+                                                bool will_retry) {
   if (!is_recording_)
     return;
   RecordCheckin("Checkin failed", base::StringPrintf(