GitLab

This change adds Windows-only logic to the PrefHashFilter such that it
verifies preferences against MACs stored in the registry. Unlike the
current tracked preference logic, this extra check does NOT reset
settings.

To avoid inconsistent state with the MACs in secure_preferences, we
clear the registry MACs before writing secure_preferences, and write
the registry MACs after the file is successfully written.

BUG=624858

Committed: https://crrev.com/4683dfcecfa72a73e00498d7c06fcf6716f8366c
Review-Url: https://codereview.chromium.org/2204943002
Cr-Original-Commit-Position: refs/heads/master@{#422240}
Cr-Commit-Position: refs/heads/master@{#422957}