Fix a flaky test and work around issue 16003 in pkg/watcher. There's an additional flaky test that this CL is not likely to fix. Additional debugging is added to help track down the cause of that flake. R=rnystrom@google.com BUG=16079 Review URL: https://codereview.chromium.org//134963007 git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/watcher@31815 260f80e4-7a28-3924-810f-c04153c831b5