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

Source/bindings/templates/union.cpp

 {% 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}}"
 
 {% from 'conversions.cpp' import v8_value_to_local_cpp_value %}
 {% macro assign_and_return_if_hasinstance(member) %}
 if (V8{{member.type_name}}::hasInstance(v8Value, isolate)) {
     {{member.cpp_local_type}} cppValue = V8{{member.type_name}}::toImpl(v8::Local<v8::Object>::Cast(v8Value));
     impl.set{{member.type_name}}(cppValue);
     return;
 }
@@ skipping 174 matching lines @@
 
 {{container.cpp_class}} NativeValueTraits<{{container.cpp_class}}>::nativeValue(v8::Isolate* isolate, v8::Local<v8::Value> value, ExceptionState& exceptionState)
 {
     {{container.cpp_class}} impl;
     V8{{container.cpp_class}}::toImpl(isolate, value, impl, exceptionState);
     return impl;
 }
 
 {% endfor %}
 } // namespace blink