To clarify: are you proposing that if Bluetooth is not present, Tether technology should be unavailable, but if Bluetooth is simply unpowered, then Tether technology should continue to be uninitialized?

Yes.

sgtm

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0de4f5aed65ec8f985d1d18a793035ead8a92a4e

commit 0de4f5aed65ec8f985d1d18a793035ead8a92a4e
Author: Kyle Horimoto <khorimoto@google.com>
Date: Wed Aug 23 23:38:21 2017

[CrOS Tether] If Bluetooth is not present, disable Tether entirely.

Previously, we assumed that if Bluetooth was not fully enabled, then
it was simply turned off by the user. In this case, we would show some
"enable Bluetooth" UI surfaces.

However, there are actually cases where Bluetooth is not present on the
system at all, so we should not display this UI. Additionally, there
are some bugs which cause Bluetooth to be hidden (crbug.com/752664).

This CL changes our logic so that Tether-related UI is never shown at
all.

Bug:  758376 , 672263
Change-Id: Id923e056524ab000e8e9901916e14b77d775c264
Reviewed-on: https://chromium-review.googlesource.com/630360
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Commit-Queue: Ryan Hansberry <hansberry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#496866}
[modify] https://crrev.com/0de4f5aed65ec8f985d1d18a793035ead8a92a4e/chrome/browser/chromeos/tether/tether_service.cc
[modify] https://crrev.com/0de4f5aed65ec8f985d1d18a793035ead8a92a4e/chrome/browser/chromeos/tether/tether_service.h
[modify] https://crrev.com/0de4f5aed65ec8f985d1d18a793035ead8a92a4e/chrome/browser/chromeos/tether/tether_service_unittest.cc
[modify] https://crrev.com/0de4f5aed65ec8f985d1d18a793035ead8a92a4e/tools/metrics/histograms/enums.xml

This bug requires manual review: We are only 11 days from stable.
Please contact the milestone owner if you have questions.
Owners: amineer@(Android), cmasso@(iOS), ketakid@(ChromeOS), govind@(Desktop)

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

Approving merge to M61 Chrome OS.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/dff3ebb898420b12213bf0dcedb092578333fb24

commit dff3ebb898420b12213bf0dcedb092578333fb24
Author: Kyle Horimoto <khorimoto@google.com>
Date: Thu Aug 24 01:11:25 2017

[CrOS Tether] If Bluetooth is not present, disable Tether entirely.

Previously, we assumed that if Bluetooth was not fully enabled, then
it was simply turned off by the user. In this case, we would show some
"enable Bluetooth" UI surfaces.

However, there are actually cases where Bluetooth is not present on the
system at all, so we should not display this UI. Additionally, there
are some bugs which cause Bluetooth to be hidden (crbug.com/752664).

This CL changes our logic so that Tether-related UI is never shown at
all.

TBR=khorimoto@google.com

(cherry picked from commit 0de4f5aed65ec8f985d1d18a793035ead8a92a4e)

Bug:  758376 , 672263
Change-Id: Id923e056524ab000e8e9901916e14b77d775c264
Reviewed-on: https://chromium-review.googlesource.com/630360
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Commit-Queue: Ryan Hansberry <hansberry@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#496866}
Reviewed-on: https://chromium-review.googlesource.com/631120
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/branch-heads/3163@{#846}
Cr-Branched-From: ff259bab28b35d242e10186cd63af7ed404fae0d-refs/heads/master@{#488528}
[modify] https://crrev.com/dff3ebb898420b12213bf0dcedb092578333fb24/chrome/browser/chromeos/tether/tether_service.cc
[modify] https://crrev.com/dff3ebb898420b12213bf0dcedb092578333fb24/chrome/browser/chromeos/tether/tether_service.h
[modify] https://crrev.com/dff3ebb898420b12213bf0dcedb092578333fb24/chrome/browser/chromeos/tether/tether_service_unittest.cc
[modify] https://crrev.com/dff3ebb898420b12213bf0dcedb092578333fb24/tools/metrics/histograms/enums.xml