Add initInternal to ViewController.

ViewController's init method was not ideal to override. On the one hand,
if you put a call super.init() first your onViewAttach method is called
before you're subclass's init.

Further, if you put your own code befer super.init(), you are still left
with the problem that your init is not automatically idempotent, and
multiple calls to #init() could result in multiple executions of your
code unless you handle it yourself.

With this change, #initInternal() is introduced, giving ViewControllers
a place to put their run-once code such that it runs before any
view-attachment callbacks are fired.

Fixes: 171472009
Test: manual
Change-Id: I2e284024c82e3f7c7b6f29f22a1ffa3c8aae9fcb