Mojo C++ bindings: custom type mapping of map

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

 class {{struct.name}}DataView {
  public:
   {{struct.name}}DataView(
       internal::{{struct.name}}_Data* data,
       mojo::internal::SerializationContext* context);
 
 {%- for pf in struct.packed.packed_fields_in_ordinal_order %}
 {%-   set kind = pf.field.kind -%}
 {%-   set name = pf.field.name -%}
-{%-   if kind|is_struct_kind or kind|is_array_kind or kind|is_string_kind %}
+{%-   if kind|is_struct_kind or kind|is_array_kind or kind|is_string_kind
+         or kind|is_map_kind %}
   template <typename UserType>
   bool Read{{name|under_to_camel}}(UserType* value) {
 {%-  if pf.min_version != 0 %}
     auto pointer = data_->header_.version >= {{pf.min_version}}
                    ? data_->{{name}}.ptr : nullptr;
 {%-  else %}
     auto pointer = data_->{{name}}.ptr;
 {%-  endif %}
     return mojo::internal::Deserialize<{{kind|unmapped_type_for_serializer}}>(
         pointer, value, context_);
   }
-{%-   elif kind|is_map_kind or kind|is_union_kind %}
+{%-   elif kind|is_union_kind %}
   bool Read{{name|under_to_camel}}({{kind|cpp_wrapper_type}}* value);
 {%-   elif kind|is_interface_kind or kind|is_any_handle_kind or
            kind|is_associated_kind %}
   {{kind|cpp_wrapper_type}} Take{{name|under_to_camel}}();
 {%-   else %}
   {{kind|cpp_wrapper_type}} {{name}}() const;
 {%-   endif %}
 {%- endfor %}
  private:
   internal::{{struct.name}}_Data* data_;
   mojo::internal::SerializationContext* context_;
 };