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The method will return the user email and whether the user's logged in,
i.e. whether the app is running on signin screen.

Adds an event that's triggered when the user focused on login
screen changes.

While here, add logic to unload the app and reset signin profile
EasyUnlockService when user logs in.

Create the signin service only if enable-easy-signin switch is set.

BUG=401634

Review URL: https://codereview.chromium.org/576343002

Cr-Commit-Position: refs/heads/master@{#296120}