Re-enable fast/events/key-events-in-input-button.html

BUG=423270
NOTRY=true
TBR=abarth@chromium.org

Review URL: https://codereview.chromium.org/699583002

git-svn-id: svn://svn.chromium.org/blink/trunk@184789 bbb929c8-8fbe-4397-9dbb-9b2b20218538