Make request_test wait for its results.

Make request_test wait for its results.

Committed: https://code.google.com/p/dart/source/detail?r=16341

[floitsch, 2012-12-19 18:29:34]

Without the expectAsync wrappers the test completes immediately on my machine
and doesn't verify the results.
Also it makes the tests run in parallel which means that the stopServer can be
executed while another test is still waiting for it.

I would guess that the flakiness is due to the a stopServer being executed too
early.

[nweiz, 2012-12-19 20:32:42]

lgtm