We can't report the "server already started" error prior to the call
to WebSocketTransformer.upgrade(), because it's possible that a
different client will successfully establish a connection during the
upgrade process. Instead, check after the call to upgrade(). This
means that if there is an error, we have to report it via a
RequestError object rather than using an HTTP error.
When we add stdio as a transport mechanism, this will have the further
advantage of allowing the "server already started" error to be
detected by code that is independent of the transport mechanism.
R=brianwilkerson@google.com
Review URL: https://codereview.chromium.org//237793002
git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@35046 260f80e4-7a28-3924-810f-c04153c831b5
paulberry@google.com
ab56da71ce