BUG= https://code.google.com/p/dart/issues/detail?id=21239
R=rnystrom@google.com

Review URL: https://codereview.chromium.org//627403002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/unittest@40968 260f80e4-7a28-3924-810f-c04153c831b5