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

sync/util/cryptographer.cc

 // Copyright (c) 2012 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 "sync/util/cryptographer.h"
 
 #include <algorithm>
 
 #include "base/base64.h"
 #include "base/basictypes.h"
@@ skipping 169 matching lines @@
   if (!nigori->InitByDerivation(params.hostname,
                                 params.username,
                                 params.password)) {
     NOTREACHED();  // Invalid username or password.
     return false;
   }
   return AddKeyImpl(nigori.Pass(), false);
 }
 
 bool Cryptographer::AddKeyFromBootstrapToken(
-    const std::string restored_bootstrap_token) {
+    const std::string& restored_bootstrap_token) {
   // Create the new Nigori and make it the default encryptor.
   std::string serialized_nigori_key = UnpackBootstrapToken(
       restored_bootstrap_token);
   return ImportNigoriKey(serialized_nigori_key);
 }
 
 bool Cryptographer::AddKeyImpl(scoped_ptr<Nigori> initialized_nigori,
                                bool set_as_default) {
   std::string name;
   if (!initialized_nigori->Permute(Nigori::Password, kNigoriKeyName, &name)) {
@@ skipping 153 matching lines @@
   if (iter == nigoris_.end())
     return std::string();
   sync_pb::NigoriKey key;
   if (!iter->second->ExportKeys(key.mutable_user_key(),
                                 key.mutable_encryption_key(),
                                 key.mutable_mac_key()))
     return std::string();
   return key.SerializeAsString();
 }
 
-bool Cryptographer::ImportNigoriKey(const std::string serialized_nigori_key) {
+bool Cryptographer::ImportNigoriKey(const std::string& serialized_nigori_key) {
   if (serialized_nigori_key.empty())
     return false;
 
   sync_pb::NigoriKey key;
   if (!key.ParseFromString(serialized_nigori_key))
     return false;
 
   scoped_ptr<Nigori> nigori(new Nigori);
   if (!nigori->InitByImport(key.user_key(), key.encryption_key(),
                             key.mac_key())) {
     NOTREACHED();
     return false;
   }
 
   if (!AddKeyImpl(nigori.Pass(), true))
     return false;
   return true;
 }
 
 }  // namespace syncer