[bindings] Include copyright block in generated code for consistency.

Source/bindings/templates/union.cpp

Index: Source/bindings/templates/union.cpp
diff --git a/Source/bindings/templates/union.cpp b/Source/bindings/templates/union.cpp
index ac015e83c7355ef860e37dd2df3b7a5d494e839a..90faae12ac9aaaad31fe79f85185469e3abf5461 100644
--- a/Source/bindings/templates/union.cpp
+++ b/Source/bindings/templates/union.cpp
@@ -1,10 +1,5 @@
 {% from 'conversions.cpp' import declare_enum_validation_variable %}
-// 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 'copyright_block.txt' %}
 #include "config.h"
 #include "{{header_filename}}"