Regression: Updating font size after opening popup once doesn't update popup

Test menulist-popup-item-style.html will fail on Mac because popup fonts can't be styled on Mac.

BUG=395613

Review URL: https://codereview.chromium.org/433513003

git-svn-id: svn://svn.chromium.org/blink/trunk@179303 bbb929c8-8fbe-4397-9dbb-9b2b20218538