Fix json_schema_compiler utils

tools/json_schema_compiler/util.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 "tools/json_schema_compiler/util.h"
 
 #include "base/values.h"
 
 namespace json_schema_compiler {
 namespace util {
@@ skipping 29 matching lines @@
 }
 void AddItemToList(const bool from, base::ListValue* out) {
   out->Append(base::Value::CreateBooleanValue(from));
 }
 void AddItemToList(const double from, base::ListValue* out) {
   out->Append(base::Value::CreateDoubleValue(from));
 }
 void AddItemToList(const std::string& from, base::ListValue* out) {
   out->Append(base::Value::CreateStringValue(from));
 }
-void AddItemToList(const linked_ptr<base::DictionaryValue> from,
+void AddItemToList(const linked_ptr<base::DictionaryValue>& from,
     base::ListValue* out) {
   out->Append(static_cast<Value*>(from->DeepCopy()));
 }
 
 }  // namespace api_util
 }  // namespace extensions