Mojo code generator: simplify how imported types and values are handled.

mojo/public/tools/bindings/generators/js_templates/union_definition.tmpl

 {%- macro union_def(union) %}
 function {{union.name}}(value) {
   this.initDefault_();
   this.initValue_(value);
 }
 
 {{tags(union)}}
 
 {{union.name}}.prototype.initDefault_ = function() {
   this.$data = null;
@@ skipping 71 matching lines @@
   }
   if (val.$tag == undefined) {
     throw new TypeError("Cannot encode unions with an unknown member set.");
   }
 
   encoder.writeUint32(16);
   encoder.writeUint32(val.$tag);
   switch (val.$tag) {
 {%-   for field in union.fields %}
     case {{union.name}}.Tags.{{field.name}}:
-{%-     if field|is_bool_field %}
+{%-     if field.kind|is_bool_kind %}
       encoder.writeUint8(val.{{field.name}} ? 1 : 0);
 {%-     else %}
       encoder.{{field.kind|union_encode_snippet}}val.{{field.name}});
 {%-     endif %}
       break;
 {%-   endfor %}
   }
   encoder.align();
 };
 {%- endmacro %}
 
 {%- macro decode(union) %}
 {{union.name}}.decode = function(decoder) {
   var size = decoder.readUint32();
   if (size == 0) {
     decoder.readUint32();
     decoder.readUint64();
     return null;
   }
 
   var result = new {{union.name}}();
   var tag = decoder.readUint32();
   switch (tag) {
 {%-   for field in union.fields %}
     case {{union.name}}.Tags.{{field.name}}:
-{%-     if field|is_bool_field %}
+{%-     if field.kind|is_bool_kind %}
       result.{{field.name}} = decoder.readUint8() ? true : false;
 {%-     else %}
       result.{{field.name}} = decoder.{{field.kind|union_decode_snippet}};
 {%-     endif %}
       break;
 {%-   endfor %}
   }
   decoder.align();
 
   return result;
@@ skipping 16 matching lines @@
 {%-     set name = union.name ~ '.' ~ field.name %}
     case {{union.name}}.Tags.{{field.name}}:
       {{validate_union_field(field, "data_offset", name)}}
       break;
 {%-   endfor %}
   }
 
   return validator.validationError.NONE;
 };
 {%- endmacro %}