Inform pywebsocket that we have sent a close frame

close-code-and-reason_wsh.py would send a close frame by a low-level API
without letting the higher levels of pywebsocket know about it.

Inform pywebsocket that it has already sent a Close frame, so it doesn't
need to send another one.

BUG=340616
TEST=layout test close-code-and-reason.html

Review URL: https://codereview.chromium.org/149063012

git-svn-id: svn://svn.chromium.org/blink/trunk@166480 bbb929c8-8fbe-4397-9dbb-9b2b20218538