Update :link/:visited style when changing href.

Previously, :link/:visited style was only updated when the href was changed
to/from a clickable anchor. The :enabled style still only needs updating
when wasLink and isLink differ.

BUG=63372

Review URL: https://codereview.chromium.org/537353002

git-svn-id: svn://svn.chromium.org/blink/trunk@181432 bbb929c8-8fbe-4397-9dbb-9b2b20218538