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This change converts callbacks from base::Bind and base::Callback to
Once/Repeating in //chromeos/components/proximity_auth.

Bug: 1007654
Change-Id: I55f3a3a1a4b30a628f106886ffa9937c01849fc7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2637412
Auto-Submit: Reilly Grant <reillyg@chromium.org>
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Commit-Queue: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845365}