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

Source/bindings/templates/union.h

 // 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!
 
 #ifndef {{macro_guard}}
 #define {{macro_guard}}
 
 {% for filename in header_includes %}
@@ skipping 48 matching lines @@
 v8::Local<v8::Value> toV8(const {{container.cpp_class}}&, v8::Local<v8::Object>, v8::Isolate*);
 
 template <class CallbackInfo>
 inline void v8SetReturnValue(const CallbackInfo& callbackInfo, {{container.cpp_class}}& impl)
 {
     v8SetReturnValue(callbackInfo, toV8(impl, callbackInfo.Holder(), callbackInfo.GetIsolate()));
 }
 
 template <>
 struct NativeValueTraits<{{container.cpp_class}}> {
-    static {{container.cpp_class}} nativeValue(const v8::Local<v8::Value>&, v8::Isolate*, ExceptionState&);
+    static {{container.cpp_class}} nativeValue(v8::Local<v8::Value>, v8::Isolate*, ExceptionState&);
 };
 
 {% endfor %}
 {% for cpp_type in nullable_cpp_types %}
 class V8{{cpp_type}}OrNull final {
 public:
     static void toImpl(v8::Isolate* isolate, v8::Local<v8::Value> v8Value, {{cpp_type}}& impl, ExceptionState& exceptionState)
     {
         {# http://heycam.github.io/webidl/#es-union #}
         {# 1. null or undefined #}
         if (isUndefinedOrNull(v8Value))
             return;
         V8{{cpp_type}}::toImpl(isolate, v8Value, impl, exceptionState);
     }
 };
 
 {% endfor %}
 } // namespace blink
 
 #endif // {{macro_guard}}