Looking at the log again,
https://chromium-review.googlesource.com/c/chromium/src/+/1173163 looks more suspicious since it is handling ChromeOS seperately.

The internal bug is here: b/117854984

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/94b2aa6c3148710e35d788a2bcb2617caff0f05d

commit 94b2aa6c3148710e35d788a2bcb2617caff0f05d
Author: Xi Han <hanxi@google.com>
Date: Fri Oct 19 12:23:28 2018

Fix: variations service not processing studies on ChromeOS.

This is caused by not setting chrome channel before initializing FeatureList in
early startup, which was introduced in CL (https://crbug.com/1173163). In this
CL, we make GetChannel() call the SetChannel() if the channel hasn't been set
yet.

Bug:  896416 
Change-Id: Id89c199779074d762f1d16edc711fedaaab66694
Reviewed-on: https://chromium-review.googlesource.com/c/1287850
Commit-Queue: Xi Han <hanxi@chromium.org>
Reviewed-by: Robert Kaplow (sloooow) <rkaplow@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601119}
[modify] https://crrev.com/94b2aa6c3148710e35d788a2bcb2617caff0f05d/chrome/browser/chromeos/chrome_browser_main_chromeos.cc
[modify] https://crrev.com/94b2aa6c3148710e35d788a2bcb2617caff0f05d/chrome/common/channel_info.h
[modify] https://crrev.com/94b2aa6c3148710e35d788a2bcb2617caff0f05d/chrome/common/channel_info_chromeos.cc

Sorry if I added the merge request early, we can merge after making sure this is working on cros dev/canary. I can update here.

Your change meets the bar and is auto-approved for M71. Please go ahead and merge the CL to branch 3578 manually. Please contact milestone owner if you have questions.
Owners: benmason@(Android), kariahda@(iOS), kbleicher@(ChromeOS), govind@(Desktop)

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

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0af3f9e9ad52d29adf6bd5613ff31f8f3f42192f

commit 0af3f9e9ad52d29adf6bd5613ff31f8f3f42192f
Author: Xi Han <hanxi@google.com>
Date: Mon Oct 22 18:01:06 2018

Fix: variations service not processing studies on ChromeOS.

This is caused by not setting chrome channel before initializing FeatureList in
early startup, which was introduced in CL (https://crbug.com/1173163). In this
CL, we make GetChannel() call the SetChannel() if the channel hasn't been set
yet.

Bug:  896416 
Change-Id: Id89c199779074d762f1d16edc711fedaaab66694
Reviewed-on: https://chromium-review.googlesource.com/c/1287850
Commit-Queue: Xi Han <hanxi@chromium.org>
Reviewed-by: Robert Kaplow (sloooow) <rkaplow@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#601119}(cherry picked from commit 94b2aa6c3148710e35d788a2bcb2617caff0f05d)
Reviewed-on: https://chromium-review.googlesource.com/c/1294389
Reviewed-by: Xi Han <hanxi@chromium.org>
Cr-Commit-Position: refs/branch-heads/3578@{#226}
Cr-Branched-From: 4226ddf99103e493d7afb23a4c7902ee496108b6-refs/heads/master@{#599034}
[modify] https://crrev.com/0af3f9e9ad52d29adf6bd5613ff31f8f3f42192f/chrome/browser/chromeos/chrome_browser_main_chromeos.cc
[modify] https://crrev.com/0af3f9e9ad52d29adf6bd5613ff31f8f3f42192f/chrome/common/channel_info.h
[modify] https://crrev.com/0af3f9e9ad52d29adf6bd5613ff31f8f3f42192f/chrome/common/channel_info_chromeos.cc

The following revision refers to this bug: 
https://chromium.googlesource.com/chromium/src.git/+/0af3f9e9ad52d29adf6bd5613ff31f8f3f42192f

Commit: 0af3f9e9ad52d29adf6bd5613ff31f8f3f42192f
Author: hanxi@google.com
Commiter: hanxi@chromium.org
Date: 2018-10-22 18:01:06 +0000 UTC

Fix: variations service not processing studies on ChromeOS.

This is caused by not setting chrome channel before initializing FeatureList in
early startup, which was introduced in CL (https://crbug.com/1173163). In this
CL, we make GetChannel() call the SetChannel() if the channel hasn't been set
yet.

Bug:  896416 
Change-Id: Id89c199779074d762f1d16edc711fedaaab66694
Reviewed-on: https://chromium-review.googlesource.com/c/1287850
Commit-Queue: Xi Han <hanxi@chromium.org>
Reviewed-by: Robert Kaplow (sloooow) <rkaplow@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#601119}(cherry picked from commit 94b2aa6c3148710e35d788a2bcb2617caff0f05d)
Reviewed-on: https://chromium-review.googlesource.com/c/1294389
Reviewed-by: Xi Han <hanxi@chromium.org>
Cr-Commit-Position: refs/branch-heads/3578@{#226}
Cr-Branched-From: 4226ddf99103e493d7afb23a4c7902ee496108b6-refs/heads/master@{#599034}