Gardening: Widen flaky crash expectation for datepicker-crash-after-keydown.html

TBR=eustas@chromium.org

Review URL: https://codereview.chromium.org/623593003

git-svn-id: svn://svn.chromium.org/blink/trunk@183094 bbb929c8-8fbe-4397-9dbb-9b2b20218538