Let me confirm with the PM about the right behavior here. I am not sure whether we should show the icon until after update completed and system reboots.

I just confirmed with hannia@. This is intended behavior.

Why do we want a different behaviour than regular update?

By regular update, do you mean that the update should be downloaded without any dialog in the middle?
The user should be notified of the update size before he make decision whether to proceed to downloading, as size matters in metered connections.

Once the user clicks "Continue" in the confirmation dialog, we should remove the update icon from the system menu until the user needs to restart.

If there are any issues during the download (error downloading, user restarts, etc), we should retry since the user has given us permission to use the cellular data.

Re #6, Ok, I see. That makes sense. I will upload a CL to fix this.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/98258cced1d9ed158af9e98706225119b6765e2d

commit 98258cced1d9ed158af9e98706225119b6765e2d
Author: weidongg <weidongg@chromium.org>
Date: Tue Jun 13 22:35:49 2017

Remove update icon after user confirms download

This CL removes update icon from system tray along with the
corresponding row in details view after user confirms download of the
update over cellular connections.

BUG= 731222 

Review-Url: https://codereview.chromium.org/2933923002
Cr-Commit-Position: refs/heads/master@{#479181}

[modify] https://crrev.com/98258cced1d9ed158af9e98706225119b6765e2d/ash/system/tray/system_tray_notifier.cc
[modify] https://crrev.com/98258cced1d9ed158af9e98706225119b6765e2d/ash/system/tray/system_tray_notifier.h
[modify] https://crrev.com/98258cced1d9ed158af9e98706225119b6765e2d/ash/system/update/tray_update.cc
[modify] https://crrev.com/98258cced1d9ed158af9e98706225119b6765e2d/ash/system/update/tray_update.h
[add] https://crrev.com/98258cced1d9ed158af9e98706225119b6765e2d/ash/system/update/update_observer.h
[modify] https://crrev.com/98258cced1d9ed158af9e98706225119b6765e2d/chrome/browser/ui/ash/system_tray_delegate_chromeos.cc
[modify] https://crrev.com/98258cced1d9ed158af9e98706225119b6765e2d/chrome/browser/ui/ash/system_tray_delegate_chromeos.h
[modify] https://crrev.com/98258cced1d9ed158af9e98706225119b6765e2d/chromeos/dbus/update_engine_client.cc
[modify] https://crrev.com/98258cced1d9ed158af9e98706225119b6765e2d/chromeos/dbus/update_engine_client.h

This bug requires manual review: M60 has already been promoted to the beta branch, so this requires manual review
Please contact the milestone owner if you have questions.
Owners: amineer@(Android), cmasso@(iOS), josafat@(ChromeOS), bustamante@(Desktop)

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

This issue has been approved for a merge. Please merge the fix to any appropriate branches as soon as possible!

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Verified on M64 build during cellular AU from 10104.0.0 to 10106.0.0