The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e82cb4b94d57fb3a8f4659eff1bc54aa3cfc1d68

commit e82cb4b94d57fb3a8f4659eff1bc54aa3cfc1d68
Author: edchin <edchin@chromium.org>
Date: Fri Apr 06 21:03:43 2018

[ios] Undo Close All button in tab grid (part 1)

This CL adds logic to show the Undo Close All button when the user
closes all tabs.
This CL does not implement the undo action.

A followup CL will add more egtests, ensuring that undo is not
available on incognito mode.

Bug:  804566 
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: Id97cb4bc3c5ad92ad622206d123a2fc37023048b
Reviewed-on: https://chromium-review.googlesource.com/998333
Commit-Queue: edchin <edchin@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548925}
[modify] https://crrev.com/e82cb4b94d57fb3a8f4659eff1bc54aa3cfc1d68/ios/chrome/app/strings/ios_strings.grd
[modify] https://crrev.com/e82cb4b94d57fb3a8f4659eff1bc54aa3cfc1d68/ios/chrome/browser/ui/tab_grid/BUILD.gn
[modify] https://crrev.com/e82cb4b94d57fb3a8f4659eff1bc54aa3cfc1d68/ios/chrome/browser/ui/tab_grid/tab_grid_constants.h
[modify] https://crrev.com/e82cb4b94d57fb3a8f4659eff1bc54aa3cfc1d68/ios/chrome/browser/ui/tab_grid/tab_grid_constants.mm
[modify] https://crrev.com/e82cb4b94d57fb3a8f4659eff1bc54aa3cfc1d68/ios/chrome/browser/ui/tab_grid/tab_grid_egtest.mm
[modify] https://crrev.com/e82cb4b94d57fb3a8f4659eff1bc54aa3cfc1d68/ios/chrome/browser/ui/tab_grid/tab_grid_egtest_util.h
[modify] https://crrev.com/e82cb4b94d57fb3a8f4659eff1bc54aa3cfc1d68/ios/chrome/browser/ui/tab_grid/tab_grid_egtest_util.mm
[modify] https://crrev.com/e82cb4b94d57fb3a8f4659eff1bc54aa3cfc1d68/ios/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm

Pri-0 bugs are critical regressions or serious emergencies, and this bug has not been updated in three days. Could you please provide an update, or adjust the priority to a more appropriate level if applicable?

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(+mardini)

Thanks for wiring this up!

It's a shame that the thumbnails aren't restored. How difficult is that to do as extra polish (I don't think it's blocking)? 

+1 regarding restoring thumbnails. I also noticed that sometimes I lose all my thumbnails. I'm not sure whether this is post-crash or post upgrade.