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

chrome/test/chromedriver/capabilities.cc

 // Copyright (c) 2013 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/test/chromedriver/capabilities.h"
 
 #include <map>
 
 #include "base/bind.h"
 #include "base/callback.h"
@@ skipping 79 matching lines @@
 Status IgnoreCapability(const base::Value& option, Capabilities* capabilities) {
   return Status(kOk);
 }
 
 Status ParseLogPath(const base::Value& option, Capabilities* capabilities) {
   if (!option.GetAsString(&capabilities->log_path))
     return Status(kUnknownError, "must be a string");
   return Status(kOk);
 }
 
-Status ParseDeviceName(std::string device_name, Capabilities* capabilities) {
+Status ParseDeviceName(const std::string& device_name,
+                       Capabilities* capabilities) {
   scoped_ptr<MobileDevice> device;
   Status status = FindMobileDevice(device_name, &device);
 
   if (status.IsError()) {
     return Status(kUnknownError,
                   "'" + device_name + "' must be a valid device",
                   status);
   }
 
   capabilities->device_metrics.reset(device->device_metrics.release());
@@ skipping 482 matching lines @@
   if (iter == logging_prefs.end() || iter->second == Log::kOff) {
     const base::DictionaryValue* chrome_options = NULL;
     if (desired_caps.GetDictionary("chromeOptions", &chrome_options) &&
         chrome_options->HasKey("perfLoggingPrefs")) {
       return Status(kUnknownError, "perfLoggingPrefs specified, "
                     "but performance logging was not enabled");
     }
   }
   return Status(kOk);
 }