Implement PasswordStoreProxyMac and SimplePasswordStoreMac.

They aren't instantiated yet in the code base. SimplePasswordStoreMac is a PasswordStore implementation on Mac in the future. PasswordStoreProxyMac is a proxy used for migration from PasswordStoreMac to SimplePasswordStoreMac.

BUG=466638

Review URL: https://codereview.chromium.org/1192963002

Cr-Commit-Position: refs/heads/master@{#335502}
10 files changed