activation-after-registration.html is no longer flaky

Fixed in Chromium r266544 <https://codereview.chromium.org/255813003/>

BUG=365252

Review URL: https://codereview.chromium.org/262493003

git-svn-id: svn://svn.chromium.org/blink/trunk@172965 bbb929c8-8fbe-4397-9dbb-9b2b20218538