Support default values for arrays of POD data types in mojom.

mojo/public/bindings/generators/cpp_templates/struct_builder_definition.tmpl

 {%- set class_name = struct.name -%}
 {%- set dtor_name = [] %}
 {%- if struct|is_struct_with_handles %}
 {%-   set _ = dtor_name.append("&internal::%s_Data_Destructor"|format(struct.name)) %}
 {%- else %}
 {%-   set _ = dtor_name.append("NULL") %}
 {%- endif %}
 
 {%- macro set_default(field) -%}
 {%-   if field.kind|is_string_kind -%}
 set_{{field.name}}(mojo::String({{field.default}}));
+{%-   elif field.kind|is_array_kind -%}
+{
+  {{field.kind|cpp_wrapper_type}}::Builder tmp({{field.default|length}});
+{%-     for element in field.default %}
+  tmp[{{loop.index0}}] = {{element}};
+{%-     endfor %}
+  set_{{field.name}}(tmp.Finish());
+}
 {%-   elif field.kind|is_object_kind -%}
 {
   {{field.kind|cpp_wrapper_type}}::Builder tmp;
   // TODO
   set_{{field.name}}(tmp.Finish());
 }
 {%-   else -%}
 set_{{field.name}}({{field.default}});
 {%-   endif %}
 {%- endmacro %}
 
 {{class_name}}::Builder::Builder(mojo::Buffer* buf)
     : data_(Data::New(buf, {{dtor_name[0]}})) {
 {%- for pf in struct.packed.packed_fields if pf.field.default %}
   {{set_default(pf.field)|indent(2)}}
 {%- endfor %}
 }
 
 {{class_name}} {{class_name}}::Builder::Finish() {
   Data* data = NULL;
   std::swap(data, data_);
   return mojo::internal::Wrap(data);
 }