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This change converts the translate model service to a
SimpleKeyedService and moves it to components which will enable
easier support beyond just browser use cases.

This change also registers the translate model service to
the optimization guide for provided necessary model files.

A future change will add loading and service the model files
to consumers of the translate model service.

Bug: 1151407
Change-Id: I4e903115c82a30757d46d75ed8d733874726d830
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2580339
Commit-Queue: Michael Crouse <mcrouse@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Reviewed-by: Trevor  Perrier <perrier@chromium.org>
Reviewed-by: Scott Little <sclittle@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Sophie Chang <sophiechang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836656}