Mojo C++ bindings: better log message for serialization warnings.

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

Index: mojo/public/tools/bindings/generators/cpp_templates/interface_definition.tmpl
diff --git a/mojo/public/tools/bindings/generators/cpp_templates/interface_definition.tmpl b/mojo/public/tools/bindings/generators/cpp_templates/interface_definition.tmpl
index 2c8a0646bb06d490ada8f815f25e4d876147f01c..fe0c1031c8e91e64ea3720d0a4dfea85e3449920 100644
--- a/mojo/public/tools/bindings/generators/cpp_templates/interface_definition.tmpl
+++ b/mojo/public/tools/bindings/generators/cpp_templates/interface_definition.tmpl
@@ -62,7 +62,8 @@ params->{{param.name}}
   MOJO_INTERNAL_DLOG_SERIALIZATION_WARNING(
       mojo::internal::IsNonNullableValidationEnabled() &&
           !params->{{param.name}}.ptr,
-      mojo::internal::VALIDATION_ERROR_UNEXPECTED_NULL_POINTER);
+      mojo::internal::VALIDATION_ERROR_UNEXPECTED_NULL_POINTER,
+      "null {{param.name}} argument");

[hansmuller, 2014/08/21 00:26:40]

It might be useful to include the name of the interface in the error message.
Likewise for the handle case below.

[yzshen1, 2014/08/21 05:57:49]

Done.

 {%-       endif %}
 {%-     elif param.kind|is_any_handle_kind %}
 {%-       if param.kind|is_interface_kind or
@@ -76,7 +77,8 @@ params->{{param.name}}
   MOJO_INTERNAL_DLOG_SERIALIZATION_WARNING(
       mojo::internal::IsNonNullableValidationEnabled() &&
           !params->{{param.name}}.is_valid(),
-      mojo::internal::VALIDATION_ERROR_UNEXPECTED_INVALID_HANDLE);
+      mojo::internal::VALIDATION_ERROR_UNEXPECTED_INVALID_HANDLE,
+      "invalid {{param.name}} argument");
 {%-       endif %}
 {%-     else %}
   params->{{param.name}} = in_{{param.name}};