Wait for Close code in close-code-and-reason

Add a call to receive_message() to the handler in close-code-and-reason_wsh.py
to ensure it does not close the connection until it has received a response from
the client.

BUG=349901
TEST=close-code-and-reason.html layout test

Review URL: https://codereview.chromium.org/192453003

git-svn-id: svn://svn.chromium.org/blink/trunk@168887 bbb929c8-8fbe-4397-9dbb-9b2b20218538