Revert 159596 "Revert 159400 "REGRESSION: Text INPUT inside a LABEL associated ...""

The revert didn't fix crbug.com/306882.

This reverts commit cb7c18183d41c63af74d461680f259e88cf934f7.
> Revert 159400 "REGRESSION: Text INPUT inside a LABEL associated ..."
>
> We believe this change caused crbug.com/306882. This is an optimistic revert to help fix the Dev branch.
>
> > REGRESSION: Text INPUT inside a LABEL associated to a radio button can't get focus by mouse press.

BUG=305751,306882
TBR=jchaffraix@chromium.org

Review URL: https://codereview.chromium.org/27631002

git-svn-id: svn://svn.chromium.org/blink/trunk@159810 bbb929c8-8fbe-4397-9dbb-9b2b20218538