Make generated field groups inherit from RefCountedCopyable.

third_party/WebKit/Source/build/scripts/templates/fields/group.tmpl

 {% from 'fields/field.tmpl' import encode, declare_storage %}
 {% from 'macros.tmpl' import print_if %}
 {% macro define_field_group_class(group): -%}
-class {{group.type_name}} : public RefCounted<{{group.type_name}}> {
+class {{group.type_name}} : public RefCountedCopyable<{{group.type_name}}> {
  public:
   static PassRefPtr<{{group.type_name}}> Create() {
     return AdoptRef(new {{group.type_name}});
   }
   PassRefPtr<{{group.type_name}}> Copy() const {
     return AdoptRef(new {{group.type_name}}(*this));
   }
 
   bool operator==(const {{group.type_name}}& other) const {
     return (
     {% for field in group.fields %}
       {{field.name}} == other.{{field.name}}{{print_if(not loop.last, ' &&')}}
     {% endfor %}
     );
   }
   bool operator!=(const {{group.type_name}}& other) const { return !(*this == other); }
 
   {% for field in group.fields %}
   {{declare_storage(field)}}
   {% endfor %}
 
  private:
   {{group.type_name}}() :
   {% for field in group.fields %}
       {{field.name}}({{encode(field, field.default_value)}}){{print_if(not loop.last, ',')}}
   {% endfor %}
   {}
 
-  ALWAYS_INLINE {{group.type_name}}(const {{group.type_name}}& other) :
-      RefCounted<{{group.type_name}}>(),
-  {% for field in group.fields %}
-      {{field.name}}(other.{{field.name}}){{print_if(not loop.last, ',')}}
-  {% endfor %}
-  {}
+  {{group.type_name}}(const {{group.type_name}}&) = default;
 };
 {%- endmacro %}