Propagate listbox onInput event after changing the HTMLSelect value

BUG=349472
R=tkent@chromium.org

Review URL: https://codereview.chromium.org/177963007

git-svn-id: svn://svn.chromium.org/blink/trunk@168894 bbb929c8-8fbe-4397-9dbb-9b2b20218538