Cleanup: Pass std::string as const reference from google_apis/ and components/gcm_driver/

google_apis/gcm/monitoring/fake_gcm_stats_recorder.h

Index: google_apis/gcm/monitoring/fake_gcm_stats_recorder.h
diff --git a/google_apis/gcm/monitoring/fake_gcm_stats_recorder.h b/google_apis/gcm/monitoring/fake_gcm_stats_recorder.h
index ba8acfdf8bfa82727e5bedd681da47cf7332a68f..e0350f4aab84f37abebfa636016fbc0d4f8c32a7 100644
--- a/google_apis/gcm/monitoring/fake_gcm_stats_recorder.h
+++ b/google_apis/gcm/monitoring/fake_gcm_stats_recorder.h
@@ -18,7 +18,8 @@ class FakeGCMStatsRecorder : 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;