[sync] Fix behavior of "Use default settings" / "Advanced" links

This CL fixes the behavior seen while switching between the "Use default
settings" / "Advanced" modes of the sync setup dialog.

BUG=316547
TEST=Switch between the "Use default settings" and "Advanced" modes. OK button must receive focus.
R=rogerta@chromium.org

Review URL: https://codereview.chromium.org/69723002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234650 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234650