GitLab

This CL extracts an interface for the AccountPickerDelegate
implementation to facilitate the account_picker package modularization
in the future.

Bug: 1149858
Change-Id: I9ddd1504da50e7feb71289a88831f1128537a28b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2542788Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Alice Wang <aliceywang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828634}