Verify correctness of classes derived from Enum.

Now that the analyzer code is no longer being translated from
Javascript, we have to maintain the enum classes manually.  These
tests will help avoid mistakes.

R=brianwilkerson@google.com, scheglov@google.com

Review URL: https://codereview.chromium.org//639293004

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41080 260f80e4-7a28-3924-810f-c04153c831b5
Splitting interop support so `dart_support.js` is no longer required.

R=jakemac@google.com

Review URL: https://codereview.chromium.org//644163002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41081 260f80e4-7a28-3924-810f-c04153c831b5