For volumes where the OS manages cached data, use the "free space" as reported by StorageStatsManager, which is the same value shown in the Settings app and other UI elements. Also, when the storage space changes significantly, invalidate anyone who was holding a cached "free space" value. Test: builds, boots Bug: 38146029 Change-Id: I4b3a484a8bf32cd137a83f1ea441beca6dc6719a