Fixed focus behaviour for radio buttons on chrome://help and chrome://settings.

If some elemenent should be focused on the page and it's a radio
button, checked one from the corresponding group is selected, instead
of the first one.

BUG=318896
TEST=manual tests on Pixel.

Review URL: https://codereview.chromium.org/79803002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236600 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236600