libsync: add support to new Sync API am: 61ab0d74d2 am: 8dc6cc921b am: 4c33794e7d Change-Id: I9c8e8ea4853712aa0196bed886a92e115cea023a Cr-Mirrored-From: https://chromium.googlesource.com/aosp/platform/system/core Cr-Mirrored-Commit: 4bd5f18f8b9c0b74294f75a99f0c544333b1df90