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

components/metrics/cloned_install_detector.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/metrics/cloned_install_detector.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/location.h"
@@ skipping 47 matching lines @@
   base::PostTaskAndReplyWithResult(
       task_runner.get(),
       FROM_HERE,
       base::Bind(&MachineIdProvider::GetMachineId, raw_id_provider_),
       base::Bind(&ClonedInstallDetector::SaveMachineId,
                  weak_ptr_factory_.GetWeakPtr(),
                  local_state));
 }
 
 void ClonedInstallDetector::SaveMachineId(PrefService* local_state,
-                                          std::string raw_id) {
+                                          const std::string& raw_id) {
   if (raw_id.empty()) {
     LogMachineIdState(ID_GENERATION_FAILED);
     local_state->ClearPref(prefs::kMetricsMachineId);
     return;
   }
 
   int hashed_id = HashRawId(raw_id);
 
   MachineIdState id_state = ID_NO_STORED_VALUE;
   if (local_state->HasPrefPath(prefs::kMetricsMachineId)) {
@@ skipping 11 matching lines @@
 
   local_state->SetInteger(prefs::kMetricsMachineId, hashed_id);
 }
 
 // static
 void ClonedInstallDetector::RegisterPrefs(PrefRegistrySimple* registry) {
   registry->RegisterIntegerPref(prefs::kMetricsMachineId, 0);
 }
 
 }  // namespace metrics