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

chromeos/tools/onc_validator/onc_validator.cc

 // Copyright (c) 2011 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 <cstdio>
 #include <iostream>
 
 #include "base/basictypes.h"
 #include "base/command_line.h"
 #include "base/files/file_path.h"
@@ skipping 64 matching lines @@
           "  %i  File is invalid.\n"
           "  %i  File couldn't be read or is not a valid JSON dictionary.\n"
           "  %i  Some command line arguments are wrong.\n",
           kStatusValid,
           kStatusWarnings,
           kStatusInvalid,
           kStatusJsonError,
           kStatusArgumentError);
 }
 
-scoped_ptr<base::DictionaryValue> ReadDictionary(std::string filename) {
+scoped_ptr<base::DictionaryValue> ReadDictionary(const std::string& filename) {
   base::FilePath path(filename);
   JSONFileValueDeserializer deserializer(path);
   deserializer.set_allow_trailing_comma(true);
 
   base::DictionaryValue* dict = NULL;
 
   std::string json_error;
   base::Value* value = deserializer.Deserialize(NULL, &json_error);
   if (!value) {
     LOG(ERROR) << "Couldn't json-deserialize file '" << filename
@@ skipping 48 matching lines @@
   } else if (type_arg == kCertificate) {
     signature = &chromeos::onc::kCertificateSignature;
   } else {
     LOG(ERROR) << "Unknown ONC type '" << type_arg << "'";
     return kStatusArgumentError;
   }
 
   chromeos::onc::Validator::Result result;
   validator.ValidateAndRepairObject(signature, *onc_object, &result);
 
-  switch(result) {
+  switch (result) {
     case chromeos::onc::Validator::VALID:
       return kStatusValid;
     case chromeos::onc::Validator::VALID_WITH_WARNINGS:
       return kStatusWarnings;
     case chromeos::onc::Validator::INVALID:
       return kStatusInvalid;
     default:
       CHECK(false);
   }
 }