Fix error handling in watcher.

BUG=
R=nweiz@google.com

Review URL: https://codereview.chromium.org//23085006

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/watcher@26156 260f80e4-7a28-3924-810f-c04153c831b5
1 file changed
tree: 7d6d0235c06e1830f946f7a6ab84b744e5d4755f
  1. pkgs/