Sent out https://chromium-review.googlesource.com/c/chromium/src/+/764512 and waiting for review. We expect this to land early next week.

Chatted with khorimoto@ via email.  Given that (i) the phone ids are already synced from Google to devices via CryptAuth, (ii) the only new info being synced is an ordering of devices, and (iii) Sync may be disabled by the user, I see no privacy concerns with this change.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/076225a61afbb52b99f342cefcd77c87a0243fc6

commit 076225a61afbb52b99f342cefcd77c87a0243fc6
Author: Kyle Horimoto <khorimoto@google.com>
Date: Tue Nov 14 23:02:17 2017

[CrOS Tether] Sync host prioritization criteria.

Host scans are prioritized according to which devices have most recently
been connected and/or have most recently replied with tether
availability. Previously, this data was stored locally on one machine,
but this change syncs these statistics via
user_prefs::PrefRegistrySyncable so that all Chromebooks share this
criteria.

The net effect is that users who sign into a new Chromebook will still
have their host scans prioritized according to their old Chromebook's
saved metadata.

Bug:  777918 , 672263
Change-Id: I04b195be784ddc77848f5ccdce1fada685bd6706
Reviewed-on: https://chromium-review.googlesource.com/764512
Commit-Queue: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Dominic Battré <battre@chromium.org>
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516480}
[modify] https://crrev.com/076225a61afbb52b99f342cefcd77c87a0243fc6/chrome/browser/chromeos/tether/tether_service.cc
[modify] https://crrev.com/076225a61afbb52b99f342cefcd77c87a0243fc6/chrome/browser/chromeos/tether/tether_service.h
[modify] https://crrev.com/076225a61afbb52b99f342cefcd77c87a0243fc6/chrome/browser/chromeos/tether/tether_service_unittest.cc
[modify] https://crrev.com/076225a61afbb52b99f342cefcd77c87a0243fc6/chromeos/components/tether/BUILD.gn
[modify] https://crrev.com/076225a61afbb52b99f342cefcd77c87a0243fc6/chromeos/components/tether/DEPS
[modify] https://crrev.com/076225a61afbb52b99f342cefcd77c87a0243fc6/chromeos/components/tether/active_host_unittest.cc
[modify] https://crrev.com/076225a61afbb52b99f342cefcd77c87a0243fc6/chromeos/components/tether/asynchronous_shutdown_object_container_impl_unittest.cc
[modify] https://crrev.com/076225a61afbb52b99f342cefcd77c87a0243fc6/chromeos/components/tether/host_scan_device_prioritizer_impl_unittest.cc
[modify] https://crrev.com/076225a61afbb52b99f342cefcd77c87a0243fc6/chromeos/components/tether/persistent_host_scan_cache_impl_unittest.cc
[modify] https://crrev.com/076225a61afbb52b99f342cefcd77c87a0243fc6/chromeos/components/tether/tether_component_impl.cc
[modify] https://crrev.com/076225a61afbb52b99f342cefcd77c87a0243fc6/chromeos/components/tether/tether_component_impl.h
[modify] https://crrev.com/076225a61afbb52b99f342cefcd77c87a0243fc6/chromeos/components/tether/tether_host_response_recorder.cc
[modify] https://crrev.com/076225a61afbb52b99f342cefcd77c87a0243fc6/chromeos/components/tether/tether_host_response_recorder.h
[modify] https://crrev.com/076225a61afbb52b99f342cefcd77c87a0243fc6/chromeos/components/tether/tether_host_response_recorder_unittest.cc
[modify] https://crrev.com/076225a61afbb52b99f342cefcd77c87a0243fc6/chromeos/components/tether/wifi_hotspot_disconnector_impl_unittest.cc

This bug requires manual review: DEPS changes referenced in bugdroid comments.
Please contact the milestone owner if you have questions.
Owners: cmasso@(Android), cmasso@(iOS), gkihumba@(ChromeOS), govind@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Can this be targeted for M64? We're already 3 weeks away from stable for such merges.

gkihumba@: Sure, we can target this for M-64 instead. This isn't an essential bug fix. Thanks!