Add support for enums within structs and interfaces to mojom.

mojo/public/bindings/sample/sample_service.mojom

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module sample {
 
 enum BarType {
   BAR_VERTICAL = 1,
   BAR_HORIZONTAL = 2,
   BAR_INVALID
@@ skipping 15 matching lines @@
   bool b @3;
   bool c @4;
   Bar bar @5;
   Bar[] extra_bars @7;
   uint8[] data @6;
   handle<message_pipe> source @9;
 };
 
 [Peer=ServiceClient]
 interface Service {
-  void Frobinate(Foo foo @0, bool baz @1, handle<message_pipe> port @2) @0;
+  enum BazOptions {
+    BAZ_REGULAR = 0,
+    BAZ_EXTRA
+  };
+  void Frobinate(Foo foo @0, int32 baz @1, handle<message_pipe> port @2) @0;
 };
 
 [Peer=Service]
 interface ServiceClient {
   void DidFrobinate(int32 result @0) @0;
 };
 
 }