Mojo bindings: Fix typemap includes.

mojo/public/tools/bindings/generators/cpp_templates/struct_serialization_declaration.tmpl

 size_t GetSerializedSize_(const {{struct.name}}Ptr& input,
                           mojo::internal::SerializationContext* context);
 void Serialize_({{struct.name}}Ptr input, mojo::internal::Buffer* buffer,
                 internal::{{struct.name}}_Data** output,
                 mojo::internal::SerializationContext* context);
 bool Deserialize_(internal::{{struct.name}}_Data* input,
                   {{struct.name}}Ptr* output,
                   mojo::internal::SerializationContext* context);
 
 {%- if struct|is_native_only_kind and struct|is_typemapped_kind %}
@@ skipping 25 matching lines @@
 
 {%-   for namespace in namespaces_as_array %}
 namespace {{namespace}} {
 {%-   endfor %}
 {%-   if variant %}
 namespace {{variant}} {
 {%-   endif %}
 
 {%- endif %}
 
-{%- if not variant and not struct|is_native_only_kind %}
+{%- if not struct|is_native_only_kind %}
 
 {# NOTE: Generated Reader instances are intentionally cheap to copy and devoid
    of heap allocations. They should stay this way. #}
 class {{struct.name}}_Reader {
  public:
   {{struct.name}}_Reader(internal::{{struct.name}}_Data* data,
                          mojo::internal::SerializationContext* context);
 
 {%-   for pf in struct.packed.packed_fields_in_ordinal_order %}
 {%-     set kind = pf.field.kind -%}
@@ skipping 90 matching lines @@
 
   static bool Deserialize(internal::{{struct.name}}_Data* input,
                           NativeType* output,
                           mojo::internal::SerializationContext* context) {
     return mojo::StructTraits<{{struct.name}}, NativeType>::Read(
         {{struct.name}}_Reader(input, context), output);
   }
 };
 
 {%- endif %}  {# not variant #}