Rewrite the Future-pipeline from the Socket to the HttpClientRequest/HttpResponse.

Rewrite the Future-pipeline from the Socket to the HttpClientRequest/HttpResponse.

Before we had two future, HttpClientRequest/HttpResponse.done and
Socket.addStream's return valud(stored as _writeDoneFuture in
    http_impl). Many issues in our code was based on the futures not
being the same, that the user will get a done event, while the socket is
still writing data on the socket.

Immidiate calls to HttpServer/HttpClient.close, after e.g. pipe, would
then destroy the socket while still having data in dart buffers.

The new approach makes sure that there is a direct future link between
the socket and the user.

BUG=

Committed: https://code.google.com/p/dart/source/detail?r=19111

[Søren Gjesse, 2013-02-27 08:23:09]

LGTM!

[Anders Johnsen, 2013-02-27 08:27:21]

Committed patchset #2 manually as r19111 (presubmit successful).