This is the current behavior in the stack view. Should we change it?

Discussing with Pete and Mardini, yes we want to change it.
It kind of made sense in the stack view as you were able to see both stacks but it makes less sense now that they are very separated.
Also both stacks have the same "Close All" string which is super confusing.

Also, when in incognito, "Close All" closes incognito tabs and leaves the regular tabs untouched (which is the current behaviour) in M68 canary with UI Refresh flag enabled. So doing the same for regular tabs would be consistent IMO. 

I agree with having "close all" apply only to what's visible. 

Load shedding bugs to Ed.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/77cd01c0b82f9dc579d8142f077868928490fb66

commit 77cd01c0b82f9dc579d8142f077868928490fb66
Author: edchin <edchin@chromium.org>
Date: Mon Jul 02 16:05:27 2018

[ios] Close all only visible panel

Previously, the close all button in regular tabs panel in tab grid would
close both the regular tabs and incognito tabs. This was the behavior
in the stack view.

This CL makes it only close the visible panel, as that makes more sense.

Bug:  845496 
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I730f7c102baaf96e983543baa42d277414339b90
Reviewed-on: https://chromium-review.googlesource.com/1120680
Reviewed-by: edchin <edchin@chromium.org>
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Commit-Queue: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571911}
[modify] https://crrev.com/77cd01c0b82f9dc579d8142f077868928490fb66/ios/chrome/browser/ui/tab_grid/tab_grid_view_controller.mm

The NextAction date has arrived: 2018-07-04

Is there more work to do here, or can this bug be closed?

Verified on chrome beta version 69.0.3497.58 on iPhone 8 plus and iPad 2018 with iOS 11.4.1. "Close All" closes only incognito or non-incognito tabs.  Looks good.