Add license files since system_api is now mirrored in Android.

BUG=b:24104607
TEST=None
Change-Id: I69544d75fa53f3ea559375199482f81ac0b934e8
Reviewed-on: https://chromium-review.googlesource.com/303537


Commit-Ready: Samuel Tan <samueltan@chromium.org>
Tested-by: Samuel Tan <samueltan@chromium.org>
Reviewed-by: Alex Deymo <deymo@chromium.org>