close-code-and-reason.html is flakily timing out, not just slow.

BUG=391068
TBR=tyoshino@chromium.org

Review URL: https://codereview.chromium.org/376833002

git-svn-id: svn://svn.chromium.org/blink/trunk@177643 bbb929c8-8fbe-4397-9dbb-9b2b20218538