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

extensions/browser/api/networking_config/networking_config_service.cc

 // Copyright 2015 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 <algorithm>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/lazy_instance.h"
 #include "base/strings/string_number_conversions.h"
@@ skipping 60 matching lines @@
   // Transform hex_ssid to uppercase.
   transform(hex_ssid.begin(), hex_ssid.end(), hex_ssid.begin(), toupper);
 
   const auto it = hex_ssid_to_extension_id_.find(hex_ssid);
   if (it == hex_ssid_to_extension_id_.end())
     return std::string();
   return it->second;
 }
 
 bool NetworkingConfigService::IsRegisteredForCaptivePortalEvent(
-    std::string extension_id) const {
+    const std::string& extension_id) const {
   return event_delegate_->HasExtensionRegisteredForEvent(extension_id);
 }
 
 bool NetworkingConfigService::RegisterHexSsid(std::string hex_ssid,
                                               const std::string& extension_id) {
   if (!IsValidNonEmptyHexString(hex_ssid)) {
     LOG(ERROR) << "\'" << hex_ssid << "\' is not a valid hex encoded string.";
     return false;
   }
 
@@ skipping 130 matching lines @@
   network_handler->managed_network_configuration_handler()->GetProperties(
       "" /* empty userhash */, service_path,
       base::Bind(&NetworkingConfigService::OnGotProperties,
                  weak_factory_.GetWeakPtr(), extension_id, guid,
                  authentication_callback),
       base::Bind(&NetworkingConfigService::OnGetPropertiesFailed,
                  weak_factory_.GetWeakPtr(), extension_id, guid));
 }
 
 }  // namespace extensions