I was able to get a patch working to expose --enable-ui-devtools in chrome:flags but it appears that you cannot remote inspect from a different machine, which is the current use case for this (i.e. inspect the CrOS system menu which cannot be done locally because the menu closes when clicking within the DevTools inspector).

Marking as available since this requires more work than I have time for currently.

Assigning to Thanh, who is making the DevTools server remotely accessible.

Thanh, please assign back to me when your piece is done and I can land the chrome:flag.

Thanks Ben. I'll ping you after 724276 landed.

CL: https://codereview.chromium.org/2928973003/

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/eafb0c0e989e157fb1ea1c90fde8157f37cc27c9

commit eafb0c0e989e157fb1ea1c90fde8157f37cc27c9
Author: bruthig <bruthig@chromium.org>
Date: Fri Jun 09 13:11:53 2017

Added --enable-ui-devtools to chrome://flags.

BUG= 678038 

Review-Url: https://codereview.chromium.org/2928973003
Cr-Commit-Position: refs/heads/master@{#478258}

[modify] https://crrev.com/eafb0c0e989e157fb1ea1c90fde8157f37cc27c9/chrome/browser/about_flags.cc
[modify] https://crrev.com/eafb0c0e989e157fb1ea1c90fde8157f37cc27c9/chrome/browser/flag_descriptions.cc
[modify] https://crrev.com/eafb0c0e989e157fb1ea1c90fde8157f37cc27c9/chrome/browser/flag_descriptions.h
[modify] https://crrev.com/eafb0c0e989e157fb1ea1c90fde8157f37cc27c9/components/ui_devtools/devtools_server.cc
[modify] https://crrev.com/eafb0c0e989e157fb1ea1c90fde8157f37cc27c9/components/ui_devtools/switches.h
[modify] https://crrev.com/eafb0c0e989e157fb1ea1c90fde8157f37cc27c9/tools/metrics/histograms/enums.xml

SocketAsyncApiFunction::OpenFirewallHole() and chromeos::FirewallHole look to be good leads...

Confirmed: It was the firewall that prevents connections and allowing connection on firewall via shell enables us to remotely connect to DevTools running on Chromebook. Next step is to see if we can somehow securely allow the connection via code.

Is there more work here?