Remove .writeStream, .consume and rewrite IOSink to correctly implement a (sane) well-defined behaviour of the .done future.

BUG=

Review URL: https://codereview.chromium.org//14028017

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@21416 260f80e4-7a28-3924-810f-c04153c831b5