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* Create ExternalAuthGoogleDelegate, owned by ExternalAuthUtils, which
  will be used to implement isGoogleSigned downstream, rather than doing
  so with an overriding subclass.
* This is patch 1/5 for providing ExternalAuthUtils as a singleton
  instead of from AppHooks.

This is a reland of
https://chromium-review.googlesource.com/c/chromium/src/+/2587429
except ExternalAuthGoogleDelegate is not yet used in ExternalAuthUtils.
That part will be implemented in the following chromium patch after
downstream implements ExternalAuthGoogleDelegateImpl.

Bug: 1154371
Change-Id: I4fd71fb81f6999be7eb26cfcb0cc121ce38f4590
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2593748Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Commit-Queue: Nick Burris <nburris@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837164}