Mojo C++ bindings: extract code shared by different variants.

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

 {%- import "interface_macros.tmpl" as interface_macros %}
 class {{interface.name}}Proxy;
 class {{interface.name}}Stub;
 
 class {{interface.name}}RequestValidator;
 {%- if interface|has_callbacks %}
 class {{interface.name}}ResponseValidator;
 {%- endif %}
 
 class {{export_attribute}} {{interface.name}} {
  public:
   static const char Name_[];
   static const uint32_t Version_ = {{interface.version}};
   static const bool PassesAssociatedKinds_ = {% if interface|passes_associated_kinds %}true{% else %}false{% endif %};
   static const bool HasSyncMethods_ = {% if interface|has_sync_methods %}true{% else %}false{% endif %};
 
   using Proxy_ = {{interface.name}}Proxy;
   using Stub_ = {{interface.name}}Stub;
 
   using RequestValidator_ = {{interface.name}}RequestValidator;
 {%- if interface|has_callbacks %}
   using ResponseValidator_ = {{interface.name}}ResponseValidator;
 {%- else %}
   using ResponseValidator_ = mojo::PassThroughFilter;
 {%- endif %}
 
 {#--- Enums #}
-{% from "enum_macros.tmpl" import enum_decl -%}
 {%- for enum in interface.enums %}
-{%-   if enum|is_native_only_kind %}
-  using {{enum.name}} = mojo::NativeEnum;
-{%-   else %}
-  {{enum_decl(enum)|indent(2)}}
-{%-   endif %}
+  using {{enum.name}} = {{enum|get_name_for_kind(flatten_nested_kind=True)}};
 {%- endfor %}
 
 {#--- Constants #}
 {%- for constant in interface.constants %}
 {%-   if constant.kind|is_integral_kind %}
   static const {{constant.kind|cpp_pod_type}} {{constant.name}} = {{constant|constant_value}};
 {%-   else %}
   static const {{constant.kind|cpp_pod_type}} {{constant.name}};
 {%-   endif %}
 {%- endfor %}
 
 {#--- Methods #}
   virtual ~{{interface.name}}() {}
 
 {%- for method in interface.methods %}
 {%    if method.response_parameters != None %}
 {%-     if method.sync %}
   // Sync method. This signature is used by the client side; the service side
   // should implement the signature with callback below.
   virtual bool {{method.name}}({{interface_macros.declare_sync_method_params("", method)}});
 {%-     endif %}
 
   using {{method.name}}Callback = {{interface_macros.declare_callback(method,
       for_blink, use_new_wrapper_types)}};
 {%-   endif %}
   virtual void {{method.name}}({{interface_macros.declare_request_params("", method)}}) = 0;
 {%- endfor %}
 };