Fix close-before-handshake-response.html

WebSocket layout test close-before-handshake-response.html failed with
the new WebSocket implementation as it did not expect an error
event. This behaviour is different from the old implementation.

Fixed by ignoring the error event.

The WebSocket API spec used to require that onerror not be fired in the
OPENING state, so the old implementation used to be correct, but the
latest spec simply requires onerror for all unclean closures, making the
new implementation correct.

BUG=339373
TEST=layout tests

Review URL: https://codereview.chromium.org/365203004

git-svn-id: svn://svn.chromium.org/blink/trunk@177549 bbb929c8-8fbe-4397-9dbb-9b2b20218538