Add a PersistentInt class. am: 76c0f6f0e8

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/18437645

Change-Id: I22fa539cc1ffe651860d2b57a7880fede8725183
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>