[mojo-bindings] Support reuse of native enum classes

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

 {#---
   Macro for enum definition, and the declaration of associated functions.
   `is_static` is relevant if this enum declaration is defined within a class, in
   which case associated functions need to be static.
 ---#}
 {%- macro enum_decl(enum, is_static=false) %}
+{%- if enum.native_only %}
+using {{enum.name}} = {{enum|cpp_wrapper_type}};
+{%- else %}
 enum class {{enum.name}} : int32_t {
-{%- for field in enum.fields %}
-{%-    if field.value %}
+{%-   for field in enum.fields %}
+{%-      if field.value %}
   {{field.name}} = {{field.value|expression_to_text}},
-{%-    else %}
+{%-      else %}
   {{field.name}},
-{%-    endif %}
-{%- endfor %}
+{%-      endif %}
+{%-   endfor %}
 };
 {{is_valid_enum_decl(enum, is_static)}}
+{% endif %}

[yzshen1, 2016/01/26 04:36:29]

nit: "{%-" (and also line 54)

 {%- endmacro %}
 
 {#--- macros for the declaration & definitions of enum-associated functions.
       Namely:
   * {enum_name}_IsValidValue:  returns true if the given enum has a valid value
                                for this generated version of enum.
 ---#}
 
 {%- macro is_valid_enum_decl(enum, is_static=false) %}
 {% if is_static %}static {% endif -%}
 bool {{enum.name}}_IsValidValue({{enum.name}} value);
 {%- endmacro %}
 
 {%- macro enum_stream_operator(enum) %}
+{%- if not enum.native_only %}
 inline std::ostream& operator<<(std::ostream& os, {{enum|get_name_for_kind}} value) {
   switch(value) {
-{%- for _, values in enum.fields|groupby('numeric_value') %}
+{%-   for _, values in enum.fields|groupby('numeric_value') %}
     case {{enum|get_name_for_kind}}::{{values[0].name}}:
       return os << "{{enum|get_name_for_kind}}::
-{%-   if values|length > 1 -%}
+{%-     if values|length > 1 -%}
       {{'{'}}
-{%-   endif -%}
+{%-     endif -%}
       {{values|map(attribute='name')|join(', ')}}
-{%-   if values|length > 1 -%}
+{%-     if values|length > 1 -%}
       {{'}'}}
-{%-   endif -%}
+{%-     endif -%}
       ";
-{%- endfor %}
+{%-   endfor %}
     default:
       return os << "Unknown {{enum|get_name_for_kind}} value: " << static_cast<int32_t>(value);
   }
 }
+{%- endif %}
 {%- endmacro %}
 
 {%- macro is_valid_enum_def(enum, class_name = '') %}
-{% if class_name != '' -%}
+{%- if not enum.native_only %}
+{%    if class_name != '' -%}
 // static
 bool {{class_name}}::
-{%- else -%}
+{%-   else -%}
 {{"bool "}}
-{%- endif -%}
+{%-   endif -%}
 {{enum.name}}_IsValidValue({{enum.name}} value) {
   switch (static_cast<int32_t>(value)) {
-{%- for enum_field in enum.fields|groupby('numeric_value') %}
+{%-   for enum_field in enum.fields|groupby('numeric_value') %}
     case {{enum_field[0]}}:
-{%- endfor %}
+{%-   endfor %}
       return true;
   }
   return false;
 }
+{% endif %}
 {%- endmacro %}