[ Merge of http://go/wvgerrit/48640 ] Usage information is saved periodically, in order to avoid excessive flash writes. This limits our session usage accuracy to within a usage save period. Saving usage information when closing a session is an improvement and addresses some failures seen with Netflix compliance tests. Bug: 74015553 Test: WV unit/integration tests Change-Id: I680aad05922f334df0611ff3933082a512f7c002