Make setRequestDowngrade @TestApi

Test: build
Bug: 134653708
Exempt-From-Owner-Approval: Already approved in
https://googleplex-android-review.git.corp.google.com/c/platform/frameworks/base/+/8350817/

Change-Id: I732aca8011490fa5815199451566ac8b0b1a2204
Merged-In: Idf99e0810e2e9040f49f06a00722567ac15bbe18
2 files changed