mojo::Serialize*_() calls now propogate/return validation errors.

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

 {%- import "interface_macros.tmpl" as interface_macros %}
 {%- import "struct_macros.tmpl" as struct_macros %}
 {%- from "enum_macros.tmpl" import is_valid_enum_def %}
 {%- from "enum_macros.tmpl" import global_enum_operators_def %}
 
 {%- set class_name = interface.name %}
 {%- set proxy_name = interface.name ~ "Proxy" %}
 {%- set namespace_as_string = "%s"|format(namespace|replace(".","::")) %}
 
 {%- macro alloc_params(struct) %}
 {%-   for param in struct.packed.packed_fields_in_ordinal_order %}
   {{param.field.kind|cpp_result_type}} p_{{param.field.name}} {};
 {%-   endfor %}
   {{struct_macros.deserialize(struct, "params", "p_%s")}}
 {%- endmacro %}
 
 {%- macro pass_params(parameters) %}
 {%-   for param in parameters %}
 {%-     if param.kind|is_move_only_kind -%}
 p_{{param.name}}.Pass()
 {%-     else -%}
 p_{{param.name}}
 {%-     endif -%}
 {%-     if not loop.last %}, {% endif %}
 {%-   endfor %}
 {%- endmacro %}
 
 {%- macro build_message(struct, struct_display_name) -%}
-  {{struct_macros.serialize(struct, struct_display_name, "in_%s", "params", "builder.buffer()")}}
+  {{struct_macros.serialize(struct, struct_display_name, "in_%s", "params", "builder.buffer()", false)}}
   params->EncodePointersAndHandles(builder.message()->mutable_handles());
 {%- endmacro %}
 
 {#--- Begin #}
 MOJO_STATIC_CONST_MEMBER_DEFINITION const char {{class_name}}::Name_[] = "{{namespace_as_string}}::{{class_name}}";
 MOJO_STATIC_CONST_MEMBER_DEFINITION const uint32_t {{class_name}}::Version_;
 
 {#--- Constants #}
 {%-  for constant in interface.constants %}
 {%-   if constant.kind|is_integral_kind %}
@@ skipping 275 matching lines @@
     default:
       break;
   }
 
   // Unrecognized message.
   ReportValidationError(
       mojo::internal::VALIDATION_ERROR_MESSAGE_HEADER_UNKNOWN_METHOD);
   return false;
 }
 {%- endif -%}