GitLab

https://codereview.chromium.org/337883003/ accidentally made this test flaky.
Fix this by calling finish from the event listener.

BUG=390445
R=yurys@chromium.org

Review URL: https://codereview.chromium.org/398413002

git-svn-id: svn://svn.chromium.org/blink/trunk@178497 bbb929c8-8fbe-4397-9dbb-9b2b20218538