Fix a typo in transformer_test.
Fix a typo in transformer_test.

R=johnniwinther@google.com, nweiz@google.com
BUG= http://dartbug.com/17527

Review URL: https://codereview.chromium.org//203163002

git-svn-id: dae132d4ca6f88932ad8a9ec3641c81ad1592b72@33797 260f80e4-7a28-3924-810f-c04153c831b5

dart-lang/observe,dart-archive/observe