Add ability to promote fields.

This adds the ability to promote private fields to public ones to
enable layoutlib to access them. This was first added in change
b556decf, but reverted in
847b0d3a. This is essentially a revert
of the change again, but without the SimpleMonthView related stuff.

Also, promote the Choreographer's field as is needed to support
animations.

Change-Id: Iee45a465c7a1cadd362c1841385941e6232e4900