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

components/gcm_driver/gcm_stats_recorder_impl.cc

 // 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.
 
 #include "components/gcm_driver/gcm_stats_recorder_impl.h"
 
 #include <deque>
 #include <vector>
 
 #include "base/format_macros.h"
@@ skipping 188 matching lines @@
                 base::StringPrintf("Delayed for %" PRId64 " msec",
                                    delay_msec));
 }
 
 void GCMStatsRecorderImpl::RecordCheckinSuccess() {
   if (!is_recording_)
     return;
   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(
       "%s.%s",
       status.c_str(),
       will_retry ? " Will retry." : "Will not retry."));
 }
 
 void GCMStatsRecorderImpl::RecordConnection(
     const std::string& event,
@@ skipping 296 matching lines @@
     const std::string& receiver_id,
     const std::string& message_id) {
   UMA_HISTOGRAM_COUNTS("GCM.IncomingSendErrors", 1);
   if (!is_recording_)
     return;
   RecordSending(app_id, receiver_id, message_id, "Received 'send error' msg",
                 std::string());
 }
 
 }  // namespace gcm