IDL: Set dictionary default values in impl constructor

Source/bindings/templates/dictionary_impl.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 "{{cpp_class}}.h"
 
 {% for filename in cpp_includes %}
 #include "{{filename}}"
 {% endfor %}
 
 namespace blink {
 
 {# Constructor #}
 {{cpp_class}}::{{cpp_class}}()
 {
+    {% for member in members if member.cpp_default_value %}
+    {{member.setter_name}}({{member.cpp_default_value}});
+    {% endfor %}
 }
 
 void {{cpp_class}}::trace(Visitor* visitor)
 {
     {% for member in members if member.is_traceable %}
     visitor->trace(m_{{member.name}});
     {% endfor %}
 }
 
 } // namespace blink