dom-ui settings: prefer to add/remove class 'hidden' rather than manipulate the style.
dom-ui settings: prefer to add/remove class 'hidden' rather than manipulate the style.

BUG=none
TEST=none
Review URL: http://codereview.chromium.org/5024004

git-svn-id: http://src.chromium.org/svn/trunk/src@66348 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 945636dd9341bb49c1100061b11cccae106478ac
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser