Many of our basic data structures are trivially movable using
memcpy() even if they are not trivially constructable, destructable
or copyable. It's worth taking advantage of this *ahem* trait.
Adding trivial_move_trait to String16 reduces appt running
time on frameworks/base/core/res by 40%!
Change-Id: I630a1a027e2d0ded96856e4ca042ea82906289fe