Fix a crash when a form control is in a past naems map of a demoted form element.

Note that we wanted to add the protector in FormAssociatedElement::setForm(),
but we couldn't do it because it is called from the constructor.


Review URL:

git-svn-id: svn:// bbb929c8-8fbe-4397-9dbb-9b2b20218538
3 files changed