Add metrics for RollbackSaveResult

- Adds enum histogram for RollbackSaveResult which represents the
result from attempting to save a users data during a rollback
- Emitting to this metric will happen via the ChromeOS Metrics Library

Bug: chromium:881341
Change-Id: I25991e754dd7186de63042222c38f94573d33bcb
Reviewed-by: Steven Holte <>
Commit-Queue: Bailey Berro <>
Cr-Commit-Position: refs/heads/master@{#623784}
2 files changed