Fix race condition with "server already started" error.

Fix race condition with "server already started" error.

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

Committed: https://code.google.com/p/dart/source/detail?r=35046

[Brian Wilkerson, 2014-04-14 21:25:43]

LGTM

https://codereview.chromium.org/237793002/diff/1/pkg/analysis_server/lib/http...
File pkg/analysis_server/lib/http_server.dart (right):

https://codereview.chromium.org/237793002/diff/1/pkg/analysis_server/lib/http...
pkg/analysis_server/lib/http_server.dart:15: import
'package:analysis_server/src/protocol.dart';
nit: I believe that we're generally keeping the imports in alphabetic order.

[Paul Berry, 2014-04-14 22:13:15]

Committed patchset #1 manually as r35046 (presubmit successful).

[jwren, 2014-04-14 22:17:43]

On 2014/04/14 21:25:43, Brian Wilkerson wrote:
> LGTM
> 
>
https://codereview.chromium.org/237793002/diff/1/pkg/analysis_server/lib/http...
> File pkg/analysis_server/lib/http_server.dart (right):
> 
>
https://codereview.chromium.org/237793002/diff/1/pkg/analysis_server/lib/http...
> pkg/analysis_server/lib/http_server.dart:15: import
> 'package:analysis_server/src/protocol.dart';
> nit: I believe that we're generally keeping the imports in alphabetic order.

LGTM