Added an 1-ms fudge factor to help de-flake a flaky test.

This is intended to help with diagnosing a flaky test on XP/Win7, and possibly overcome the flakiness.

BUG=282620

Review URL: https://chromiumcodereview.appspot.com/23449022

git-svn-id: svn://svn.chromium.org/blink/trunk@157305 bbb929c8-8fbe-4397-9dbb-9b2b20218538