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

mojo/public/bindings/pylib/generate/mojom_generator.py

Index: mojo/public/bindings/pylib/generate/mojom_generator.py
diff --git a/mojo/public/bindings/pylib/generate/mojom_generator.py b/mojo/public/bindings/pylib/generate/mojom_generator.py
index 24901aceda57883029d07ad760232b581c33dc1a..1148764d635c181e0de0425a675ebef2cc6f0f6e 100644
--- a/mojo/public/bindings/pylib/generate/mojom_generator.py
+++ b/mojo/public/bindings/pylib/generate/mojom_generator.py
@@ -53,6 +53,14 @@ def VerifyTokenType(token, expected):
     raise Exception("Expected token type '%s'. Got '%s'." %
         (expected, token[0]))
 
+def ExpressionMapper(expression, mapper):
+  if isinstance(expression, tuple) and expression[0] == 'EXPRESSION':
+    result = []
+    for each in expression[1]:
+      result.extend(ExpressionMapper(each, mapper))
+    return result
+  return [mapper(expression)]
+
 class Generator(object):
   # Pass |output_dir| to emit files to disk. Omit |output_dir| to echo all
   # files to stdout.