Fix accessibility delegation

Ensures that delegate code is run last. Previously, calling the super
method from an accessibility delegate set on a widget would only run
code in the widget's parent. Next, the delegate code would run. Finally,
the widget's code would run. As a result, the widget code would override
any data supplied by the delegate.

By moving all overridden code to internal methods, we ensure that the
call chain for super includes the widget's parent code followed by the
widget's code. The delegate code will always run last.

BUG: 17641433
Change-Id: Ib9d403156c1fc4fb04f65f3c126d1277a44b3740