[Password Manager] [OSCrypt] Deleting undecryptable logins from database.

This CL include following changes:
- Added method to LoginDatabase that deleted entries which fail decryption process on MacOS.
- Added tests for the above changes.
- Added method SetBackendLocked to OSCryptMocker to test behavior when Keychain on Mac is locked.

Change-Id: I2173467771457d32d2b2d953d4e27d888965e475
Bug: 791541
Reviewed-on: https://chromium-review.googlesource.com/1146642
Commit-Queue: Tonko Sabolčec <tsabolcec@google.com>
Reviewed-by: Christos Froussios <cfroussios@chromium.org>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578357}
7 files changed