Seed the account tracker with gaia_id/email before performing sign in.
This CL is part of moving chrome to using gaia ids to unique identity google accounts internally instead of using email address, since the later can change over the life of an account and because there are different normalizations of the email, which makes comparisons difficult.
When chrome finally switches over, it needs a way to map gaia ids to show in UI. For this reason, making sure the mapping exists before sign-in happens is important.
This CL represents step 5 in my design doc for this migration:
https://docs.google.com/a/google.com/document/d/1WIXhEalgwvp3ouG4uTLy8YQOeqxa_zPHsv6wtBu3kWQ/edit#
BUG=341408
Review URL: https://codereview.chromium.org/
705603004
Cr-Commit-Position: refs/heads/master@{#303475}