[mojo-bindings] Support reuse of native enum classes

mojo/public/tools/bindings/pylib/mojom/generate/data.py

Index: mojo/public/tools/bindings/pylib/mojom/generate/data.py
diff --git a/mojo/public/tools/bindings/pylib/mojom/generate/data.py b/mojo/public/tools/bindings/pylib/mojom/generate/data.py
index 60ae1e0d4c55e3df67b6db1c6cfc508696505527..6fc77ae9e1c951081b5e3ea6ea47912244421b50 100644
--- a/mojo/public/tools/bindings/pylib/mojom/generate/data.py
+++ b/mojo/public/tools/bindings/pylib/mojom/generate/data.py
@@ -397,6 +397,7 @@ def ResolveNumericEnumValues(enum_fields):
 def EnumFromData(module, data, parent_kind):
   enum = mojom.Enum(module=module)
   enum.name = data['name']
+  enum.native_only = data['native_only']
   name = enum.name
   if parent_kind:
     name = parent_kind.name + '.' + name
@@ -404,11 +405,18 @@ def EnumFromData(module, data, parent_kind):
   enum.parent_kind = parent_kind
   enum.fields = map(
       lambda field: EnumFieldFromData(module, enum, field, parent_kind),
-      data['fields'])
+      data['fields']) if not enum.native_only else []
   enum.attributes = data.get('attributes')
   ResolveNumericEnumValues(enum.fields)
 
   module.kinds[enum.spec] = enum
+
+  # Enforce that a [native=True] attribute is set to make native-only enum
+  # declarations more explicit.
+  if enum.native_only:
+    if not enum.attributes or not enum.attributes.get('native', False):
+      raise Exception("Native-only enum declarations must include a " +
+                      "native=True attribute.")
   return enum
 
 def ConstantFromData(module, data, parent_kind):