This is just changing the ui. There is no change in functionality yet.
Traditionally if you could not submit the change, the submit button
was just not there (visible=false). This behavior is still there if
atomic topics are enabled and the submission is prevented by the
current change. That doesn't break with the history.
If however another change in the same topic blocks submission the
submit button is shown, but disabled. It would be a nice follow up
change to give the reason to the user what exactly blocks submission,
but that blocker may not be accessible for the current user.
Designing a precise and helpful error message, which doesn't leak
any secrets is done in a follow up commit.
Change-Id: Ib32a4511a0308da32a8c5d1c7b1a6f124a03576e
ec65f84869