You probably want to add a trivial method to chromeos::PowerPolicyController in Chrome that updates an e.g. avoid_shutdown_on_lid_closed_for_user_migration_ bool member and sends an updated policy, and then call it at the beginning and end of the migration. I'm happy to do code reviews for this or offer additional guidance.

fukino@, is this enough information to get this done?
We'd like this in the next dev push if possible as it's affecting live metrics and users.

Curious as to why suspending will help here?  There is no code execution that happens while the system is suspended.

The bug is that we're shutting down during migration and shutdown unmounts file system while file copies are happening and that probably is one of the cause of errors being sent in (1% of migrations are reporting NOT_FOUND).

suspend/resume instead of shutting down makes it behave better.

Not suspending (or shutting down) was the original UX spec, I heard second hand concerns on heat (not sure if I buy that argument but it's not a showstopper if we suspend/resumed).

OK. Keep in mind that the system can run out of battery while suspended.

Yep, poweroff doesn't actually cause any real user-visible damage, mostly just raises false alarms in the logs and degrades the user experience a bit (they have to re-login to resume the migration)

do we have a better understanding now? any updates?

There's an in-progress code review at https://codereview.chromium.org/2907773002/.

dspaid sent out an update since fukino's ooo https://codereview.chromium.org/2912763003/

https://codereview.chromium.org/2912763003/
is submitted. TODO: merge request to M60

don't you usually keep the bug open to do merge request? 

I don't know that the status matters, but the request label does. :-)

It's usually OK to mark fixed before merging to branches.

Your change meets the bar and is auto-approved for M60. Please go ahead and merge the CL to branch 3112 manually. Please contact 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

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f4f285abd6c1b70b7ea16e6ed03f68e56cbc5df6

commit f4f285abd6c1b70b7ea16e6ed03f68e56cbc5df6
Author: Kazuhiro Inaba <kinaba@chromium.org>
Date: Mon Jun 05 02:39:52 2017

cros: Prevent shut down on lid-close during migration.

In the login screen, the system will shut down on lid close.
Although we ask users not to close the lid during the migration, it
should be better to change the lid-close action to SUSPEND during
migration.

BUG= 726229 
TEST=out/Release/chromeos_unittests --gtest_filter=PowerPolicyControllerTest.*

Review-Url: https://codereview.chromium.org/2912763003
Cr-Original-Commit-Position: refs/heads/master@{#476091}
Review-Url: https://codereview.chromium.org/2922913002 .
Cr-Commit-Position: refs/branch-heads/3112@{#138}
Cr-Branched-From: b6460e24cf59f429d69de255538d0fc7a425ccf9-refs/heads/master@{#474897}

[modify] https://crrev.com/f4f285abd6c1b70b7ea16e6ed03f68e56cbc5df6/chrome/browser/ui/webui/chromeos/login/encryption_migration_screen_handler.cc
[modify] https://crrev.com/f4f285abd6c1b70b7ea16e6ed03f68e56cbc5df6/chromeos/dbus/power_policy_controller.cc
[modify] https://crrev.com/f4f285abd6c1b70b7ea16e6ed03f68e56cbc5df6/chromeos/dbus/power_policy_controller.h
[modify] https://crrev.com/f4f285abd6c1b70b7ea16e6ed03f68e56cbc5df6/chromeos/dbus/power_policy_controller_unittest.cc