Mojo C++ bindings: support enum validation.

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

Index: mojo/public/tools/bindings/pylib/mojom/generate/module.py
diff --git a/mojo/public/tools/bindings/pylib/mojom/generate/module.py b/mojo/public/tools/bindings/pylib/mojom/generate/module.py
index 43476097216f233cec5b0249174f5d618a10ad7b..cb0a0108eaeda79c35b9beaaacdd195ab4799fbd 100644
--- a/mojo/public/tools/bindings/pylib/mojom/generate/module.py
+++ b/mojo/public/tools/bindings/pylib/mojom/generate/module.py
@@ -131,6 +131,7 @@ PRIMITIVES = (
 
 
 ATTRIBUTE_MIN_VERSION = 'MinVersion'
+ATTRIBUTE_EXTENSIBLE = 'Extensible'
 
 
 class NamedValue(object):
@@ -445,6 +446,11 @@ class Enum(Kind):
     self.fields = []
     self.attributes = attributes
 
+  @property
+  def extensible(self):
+    return self.attributes.get(ATTRIBUTE_EXTENSIBLE, False) \
+        if self.attributes else False
+
 
 class Module(object):
   def __init__(self, name=None, namespace=None, attributes=None):