Add skipThenUpdateDisplay public method and use it for shouldSkip.

* Uses private guiders._followShouldSkip method to walk the shouldSkip chain.
* Use null object pattern for shouldSkip so it can call the method unconditionally.
* Also fix misleading var declaration.

Change-Id: I00b62bb5e3e5b5f0e60248b90ff2ef6e055d342f