rAc: fix verify cvv codepath so that the card generation overlay is
shown properly after verifying a CVV.

Also fix a bug in the layout of |message_stack_| which was for some reason only apparent in the CVV codepath. Remove vestigial ability to display multiple messages.

BUG=306304

Review URL: https://codereview.chromium.org/55593002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232534 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232534