Revert r38549, r38552, and r38557.

It's currently too difficult to include a third party package for it to be
worthwhile for this use case.

R=alanknight@google.com

Review URL: https://codereview.chromium.org//419683002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/pool@38564 260f80e4-7a28-3924-810f-c04153c831b5