[bindings] Pass v8::Local<v8::Value> by value in NativeValueTraits<T>::nativeValue()

Source/bindings/templates/dictionary_v8.cpp

 // Copyright 2014 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.
 
 // This file has been auto-generated by {{code_generator}}. DO NOT MODIFY!
 
 #include "config.h"
 #include "{{v8_original_class}}.h"
 
 {% for filename in cpp_includes if filename != '%s.h' % v8_class %}
@@ skipping 89 matching lines @@
         dictionary->Set(v8String(isolate, "{{member.name}}"), {{member.cpp_value_to_v8_value}});
     {% if member.v8_default_value %}
     } else {
         dictionary->Set(v8String(isolate, "{{member.name}}"), {{member.v8_default_value}});
     {% endif %}
     }
 
     {% endfor %}
 }
 
-{{cpp_class}} NativeValueTraits<{{cpp_class}}>::nativeValue(const v8::Local<v8::Value>& value, v8::Isolate* isolate, ExceptionState& exceptionState)
+{{cpp_class}} NativeValueTraits<{{cpp_class}}>::nativeValue(v8::Local<v8::Value> value, v8::Isolate* isolate, ExceptionState& exceptionState)
 {
     {{cpp_class}} impl;
     {{v8_class}}::toImpl(isolate, value, impl, exceptionState);
     return impl;
 }
 
 } // namespace blink