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

sync/test/engine/test_id_factory.h

 // 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.
 //
 // A tool making it easier to create IDs for unit testing.
 
 #ifndef SYNC_TEST_ENGINE_TEST_ID_FACTORY_H_
 #define SYNC_TEST_ENGINE_TEST_ID_FACTORY_H_
 
 #include <string>
@@ skipping 18 matching lines @@
   static syncable::Id FromNumber(int64 value) {
     if (value == 0)
       return root();
     else if (value < 0)
       return syncable::Id::CreateFromClientString(base::Int64ToString(value));
     else
       return syncable::Id::CreateFromServerId(base::Int64ToString(value));
   }
 
   // Create a local ID from a name.
-  static syncable::Id MakeLocal(std::string name) {
+  static syncable::Id MakeLocal(const std::string& name) {
     return syncable::Id::CreateFromClientString(std::string("lient ") + name);
   }
 
   // Create a server ID from a string name.
-  static syncable::Id MakeServer(std::string name) {
+  static syncable::Id MakeServer(const std::string& name) {
     return syncable::Id::CreateFromServerId(std::string("erver ") + name);
   }
 
   // Autogenerate a fresh local ID.
   syncable::Id NewLocalId() {
     return syncable::Id::CreateFromClientString(
         std::string("_auto ") + base::IntToString(-next_value()));
   }
 
   // Autogenerate a fresh server ID.
   syncable::Id NewServerId() {
     return syncable::Id::CreateFromServerId(
         std::string("_auto ") + base::IntToString(next_value()));
   }
 
  private:
   int next_value() {
     return next_value_++;
   }
   int next_value_;
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_TEST_ENGINE_TEST_ID_FACTORY_H_