Start the migration of passwords from the Keychain.

Design doc: https://docs.google.com/a/google.com/document/d/1A8ZG16bLuUH1u21K0GoABKz_wpz1kchXMnMlpmq_ecA/edit?usp=sharing

BUG=466638

Review URL: https://codereview.chromium.org/1213043003

Cr-Commit-Position: refs/heads/master@{#337842}
17 files changed