Use MessageUtils instead of hardcoded strings in policyNameOf.

This makes the code easier to maintain because we do not need to
manually add string representations, and because it will throw at
static initialization time if the clas contains duplicate
POLICY_xxx values. The memory overhead is likely negligible.

Bug: 216567577
Test: new coverage in FullScoreTest
Change-Id: Iab23d414c8e28ff7f26060ad44fa996f277d361f
2 files changed