Make ComputedStyleBase use MemberCopy when copying pointer fields.

third_party/WebKit/Source/build/scripts/templates/ComputedStyleBase.h.tmpl

 {% from 'macros.tmpl' import license, print_if %}
 {% from 'fields/field.tmpl' import encode, getter_expression, setter_expression, declare_storage, fieldwise_compare, fieldwise_copy, fieldwise_diff, fieldwise_pointer_compare_inherited %}
 {% from 'fields/group.tmpl' import define_field_group_class %}
 {{license()}}
 
 #ifndef ComputedStyleBase_h
 #define ComputedStyleBase_h
 
 #include "core/style/ComputedStyleConstants.h"
 #include "core/CoreExport.h"
 #include "core/style/DataRef.h"
+#include "core/style/MemberCopy.h"
 #include "core/style/StyleDifference.h"
 #include "platform/wtf/SizeAssertions.h"
 #include "core/layout/LayoutTheme.h"
 {% for path in include_paths %}
 #include "{{path}}"
 {% endfor %}
 
 {# Each field template has macros that we can call to generate specific
    aspects of the field (e.g. getters, setters).
 #}
@@ skipping 200 matching lines @@
 
  private:
   {% for field in computed_style.fields %}
   {{declare_storage(field)}}
   {% endfor %}
 };
 
 } // namespace blink
 
 #endif // ComputedStyleBase_h