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- Return canonicalized email from GetUserEmail because sign-in
  manager gives back the Gaia email which is not necessarily the
  same as the one used on the login screen;
- Sign-in manager gives empty user email when underlying refresh token
  is revoked. Bail out in this case.

BUG=489890

Review URL: https://codereview.chromium.org/1149873003

Cr-Commit-Position: refs/heads/master@{#330890}