Mojo C++ bindings: introduce an optional array to store transferred interface IDs in messages.

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

 {#  TODO(yzshen): Make these templates more readable. #}
 
 {#  Computes the serialized size for the specified struct.
     |struct| is the struct definition.
     |input_field_pattern| should be a pattern that contains one string
     placeholder, for example, "input->%s", "p_%s". The placeholder will be
     substituted with struct field names to refer to the input fields.
     |context| is the name of the serialization context.
     |input_may_be_temp| indicates whether any input may be temporary obejcts.
     We need to assign temporary objects to local variables before passing it to
     Serializer, because it is illegal to pass temporary objects as non-const
     references.
     This macro is expanded to compute seriailized size for both:
     - user-defined structs: the input is an instance of the corresponding struct
       wrapper class.
     - method parameters/response parameters: the input is a list of
       arguments.
     It declares |size| of type size_t to store the resulting size. #}
 {%- macro get_serialized_size(struct, input_field_pattern, context,
                               input_may_be_temp=False) -%}
   size_t size = sizeof({{struct|get_qualified_name_for_kind(internal=True)}});
-{%-   for pf in struct.packed.packed_fields_in_ordinal_order if pf.field.kind|is_object_kind %}
+{%-   for pf in struct.packed.packed_fields_in_ordinal_order
+          if pf.field.kind|is_object_kind or pf.field.kind|is_associated_kind %}
 {%-     set name = pf.field.name -%}
 {%-     set kind = pf.field.kind -%}
 {%-     set original_input_field = input_field_pattern|format(name) %}
 {%-     set input_field = "in_%s"|format(name) if input_may_be_temp
                                                else original_input_field %}
 {%-     if input_may_be_temp %}
   decltype({{original_input_field}}) in_{{name}} = {{original_input_field}};
 {%-     endif %}
 
 {%-     set serializer_type = kind|unmapped_type_for_serializer %}
@@ skipping 118 matching lines @@
 {%-     elif kind|is_any_handle_kind %}
   {{output_field}} = {{input}}.Take{{name|under_to_camel}}();
 {%-     elif kind|is_any_interface_kind %}
   {{output_field}} =
       {{input}}.Take{{name|under_to_camel}}<decltype({{output_field}})>();
 {%-     else %}
   {{output_field}} = {{input}}.{{name}}();
 {%-     endif %}
 {%-   endfor %}
 {%- endmacro %}