Mojo: Add support for constants to the IDL compiler.

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

 {%- macro set_default(module, kind, value, depth) -%}
 {#--- Strings ---#}
 {%-   if kind|is_string_kind -%}
 {{caller(value|expression_to_text(module))}}
 {#--- Arrays ---#}
 {%-   elif kind|is_array_kind %}
 {%-     set _ = value|verify_token_type("ARRAY") %}
 {
   var tmp{{depth}} = [];
 {%-     for element in value[1] %}
@@ skipping 22 matching lines @@
 {%-   endfor -%}
   {{caller("tmp" ~ depth)|indent(2)}}
 }
 {#--- POD types ---#}
 {%-   else -%}
 {{caller(value|expression_to_text(module))}}
 {%-   endif %}
 {%- endmacro %}
 
 {#--- Begin #}
-{#--- Enums. We must define these before the constructor because they
-      may be used there. Later, we alias these to be class static variables. #}
+  function {{struct.name}}() {
+    this.initDefaults_();
+  }
+
+{#--- Enums #}
 {%- from "enum_definition.tmpl" import enum_def %}
 {%  for enum in struct.enums %}
-  var {{enum_def("%s_%s"|format(struct.name, enum.name), enum, module)}}
+  {{enum_def("%s.%s"|format(struct.name, enum.name), enum, module)}}
 {%  endfor %}
 
-{#--- Constructor #}
-  function {{struct.name}}() {
+{#--- Constants #}
+{%  for constant in struct.constants %}
+  {{struct.name}}.{{constant.name}} = {{constant.value|expression_to_text(module)}};
+{%  endfor %}
+
+{#--- Set up defaults #}
+  {{struct.name}}.prototype.initDefaults_ = function() {
 {%- for packed_field in struct.packed.packed_fields %}
 {%- if packed_field.field.default %}
 {%-   filter indent(4) %}
 {%-     call(result) set_default(module, packed_field.field.kind, packed_field.field.default, 0) %}
 this.{{packed_field.field.name}} = {{result}};
 {%-     endcall %}
 {%-   endfilter %}
 {%- else %}
     this.{{packed_field.field.name}} = {{packed_field.field|default_value}};
 {%- endif %}
 {%- endfor %}
-  }
-
-{#--- Alias any Struct_Enum enums to Struct.Enum #}
-{%  for enum in struct.enums %}
-  {{struct.name}}.{{enum.name}} = {{struct.name}}_{{enum.name}};
-{%- endfor %}
+  };
 
 {#--- Encoding and decoding #}
 
   {{struct.name}}.encodedSize = codec.kStructHeaderSize + {{struct.packed|payload_size}};
 
   {{struct.name}}.decode = function(decoder) {
     var packed;
     var val = new {{struct.name}}();
     var numberOfBytes = decoder.readUint32();
     var numberOfFields = decoder.readUint32();
@@ skipping 30 matching lines @@
 {%-   else %}
 {%-     for packed_field in byte.packed_fields %}
     encoder.{{packed_field.field.kind|encode_snippet}}val.{{packed_field.field.name}});
 {%-     endfor %}
 {%-   endif %}
 {%-   if byte.is_padding %}
     encoder.skip(1);
 {%-   endif %}
 {%- endfor %}
   };