Fix list_path_observer, temporarily add a test for it, but we'll likely remove it in the future since it's no longer in observe-js. [email protected] Review URL: https://codereview.chromium.org//357003002 git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/observe@37774 260f80e4-7a28-3924-810f-c04153c831b5