Close notification guts after applying changes

ChannelEditorDialogController now tells interested parties about the
fact that it wants to dismiss. NotificationInfo also can close itself
without saving changes

Test: disable top channel in dialog, watch the guts close and
notification disappear
Bug: 133182818

Change-Id: I70adc7dc0d6b9a8a207cdff0b28b281fbd24e18a