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

chrome/browser/media_galleries/media_galleries_scan_result_controller.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 "chrome/browser/media_galleries/media_galleries_scan_result_controller.h"
 
 #include <algorithm>
 #include <list>
 
 #include "base/bind.h"
@@ skipping 311 matching lines @@
 void MediaGalleriesScanResultController::OnPreferenceUpdate(
     const std::string& extension_id) {
   if (extension_id == extension_->id()) {
     UpdateScanResultsFromPreferences(preferences_, extension_,
                                      results_to_remove_, &scan_results_);
     dialog_->UpdateGalleries();
   }
 }
 
 void MediaGalleriesScanResultController::OnRemovableDeviceUpdate(
-    const std::string device_id) {
+    const std::string& device_id) {
   for (ScanResults::const_iterator it = scan_results_.begin();
        it != scan_results_.end();
        ++it) {
     if (it->second.pref_info.device_id == device_id) {
       dialog_->UpdateGalleries();
       return;
     }
   }
 }
 
@@ skipping 35 matching lines @@
     MediaGalleriesPreferences* /*prefs*/,
     MediaGalleryPrefId /*pref_id*/) {
   OnPreferenceUpdate(extension_->id());
 }
 
 void MediaGalleriesScanResultController::OnGalleryInfoUpdated(
     MediaGalleriesPreferences* /*prefs*/,
     MediaGalleryPrefId /*pref_id*/) {
   OnPreferenceUpdate(extension_->id());
 }