I have a CL to do this here: https://chromium-review.googlesource.com/c/chromiumos/platform/tremplin/+/1234280

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/platform/tremplin/+/9f40b7d41ba132f84c2d6c5d9874df77dbafa13f

commit 9f40b7d41ba132f84c2d6c5d9874df77dbafa13f
Author: Stephen Barber <smbarber@chromium.org>
Date: Fri Sep 21 04:30:12 2018

tremplin: move shared directory to /ChromeOS

Also move the config into the default profile.

BUG= chromium:886546 
TEST=boot container; check for /ChromeOS

Change-Id: I7ef10177acfa21f32191493da946d6ea250e0373
Reviewed-on: https://chromium-review.googlesource.com/1234280
Commit-Ready: Stephen Barber <smbarber@chromium.org>
Tested-by: Stephen Barber <smbarber@chromium.org>
Reviewed-by: Chirantan Ekbote <chirantan@chromium.org>
Reviewed-by: Joel Hockey <joelhockey@chromium.org>

[modify] https://crrev.com/9f40b7d41ba132f84c2d6c5d9874df77dbafa13f/src/chromiumos/tremplin/main.go
[modify] https://crrev.com/9f40b7d41ba132f84c2d6c5d9874df77dbafa13f/src/chromiumos/tremplin/tremplin.go

This should be fixed in the next component update.

This directory has now changed from /ChromeOS to /mnt/chromeos

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/platform/tremplin/+/f0cd5f58e9693471d6059d0e94d773439472bde4

commit f0cd5f58e9693471d6059d0e94d773439472bde4
Author: Joel Hockey <joelhockey@chromium.org>
Date: Wed Oct 31 15:17:30 2018

tremplin: move shared directory to /mnt/chromeos

BUG= chromium:886546 
TEST=boot container; check for /mnt/chromeos

Change-Id: Ia1605a91032e21ef0fc2cae17e38d4a9327b6803
Reviewed-on: https://chromium-review.googlesource.com/1309437
Commit-Ready: Joel Hockey <joelhockey@chromium.org>
Tested-by: Joel Hockey <joelhockey@chromium.org>
Reviewed-by: Stephen Barber <smbarber@chromium.org>
Reviewed-by: Joel Hockey <joelhockey@chromium.org>

[modify] https://crrev.com/f0cd5f58e9693471d6059d0e94d773439472bde4/src/chromiumos/tremplin/main.go

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/027a69b8a20bea0a89bc2db8a6a23bedd40178d9

commit 027a69b8a20bea0a89bc2db8a6a23bedd40178d9
Author: Joel Hockey <joelhockey@chromium.org>
Date: Thu Nov 01 00:03:48 2018

Crostini container mount dir changed to /mnt/chromeos

Bug:  886546 
Change-Id: Ice466abf61544783407bac9601b23a01982c4055
Reviewed-on: https://chromium-review.googlesource.com/c/1309378
Reviewed-by: Timothy Loh <timloh@chromium.org>
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604455}
[modify] https://crrev.com/027a69b8a20bea0a89bc2db8a6a23bedd40178d9/chrome/browser/chromeos/crostini/crostini_util.cc
[modify] https://crrev.com/027a69b8a20bea0a89bc2db8a6a23bedd40178d9/chrome/browser/chromeos/file_manager/path_util_unittest.cc