Integrate PasswordStoreProxyMac instead of PasswordStoreMac.

For now PasswordStoreProxyMac is just a wrapper around PasswordStoreMac.
The goal is to remove the Keychain integration on Mac. 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/1200603003

Cr-Commit-Position: refs/heads/master@{#336130}
15 files changed