Fix bug with using enums as default values in mojom. We were previously

mojo/public/bindings/generators/js_templates/enum_definition.tmpl

Index: mojo/public/bindings/generators/js_templates/enum_definition.tmpl
diff --git a/mojo/public/bindings/generators/js_templates/enum_definition.tmpl b/mojo/public/bindings/generators/js_templates/enum_definition.tmpl
index a87db5c45b19c61d6ab15e224d6ba9d8232f5c25..653cfaacbd0299c8ca18df43fa3131ecc80e7339 100644
--- a/mojo/public/bindings/generators/js_templates/enum_definition.tmpl
+++ b/mojo/public/bindings/generators/js_templates/enum_definition.tmpl
@@ -1,12 +1,14 @@
-{%- macro enum_def(enum_init, enum) %}
-  {{enum_init}} = {
-{%- set next_value = 0 %}
+{%- macro enum_def(enum_name, enum, module) -%}
+  {{enum_name}} = {};
+
+{%- set prev_enum = 0 %}
 {%- for field in enum.fields %}
 {%-   if field.value %}
-{%-     set next_value = field.value|int  %}
+  {{enum_name}}.{{field.name}} = {{field.value|expression_to_text(module)}};
+{%-   elif loop.first %}
+  {{enum_name}}.{{field.name}} = 0;
+{%-   else %}
+  {{enum_name}}.{{field.name}} = {{enum_name}}.{{enum.fields[loop.index0 - 1].name}} + 1;
 {%-   endif %}
-    {{field.name}}: {{next_value}},
-{%-   set next_value = next_value + 1 %}
 {%- endfor %}
-  };
 {%- endmacro %}