To clarify:  The extension seems to have been converted from a userscript initially, on the extension author's PC, which resulted in the flag being added. So they acted 100% morally.

Interesting, thanks for the report!

[security-sheriffing] I repro'd this on Linux M63.  I expect this could be used by UwSy extensions, and we should test if it affects side-loaded extensions as well.

proberge -- Can you take this?

Yes, I'll take care of it.

To partially protect users from side-loaded extensions, we should put the protections in Chrome instead of during the CWS upload.

This is only a partial protection: binary UwS may still be able to modify the extension settings in the pref file to add the flag.

Alternatively, we could try removing the converted-from-user-script flag and make these extensions behave the same UI-wise as other extensions. I don't know if this is reasonable - @devlin do we have some documentation about the TYPE_USER_SCRIPT extensions? There's some weird related code like set_emulate_greasemonkey. Also weird: Manifest::Type Extension::GetType(). 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b4de3afbcc0a25e6043ba7c1a2b5ef60101d0694

commit b4de3afbcc0a25e6043ba7c1a2b5ef60101d0694
Author: proberge <proberge@chromium.org>
Date: Mon Jan 29 16:40:57 2018

Make ExtensionActionHandler manifest handler parse userscript extensions

This effectively makes user script extensions show up in the tab bar.

Bug:  801861 
Change-Id: I8fd4df034eee07403cda0a0eabef2d68ff5f272a
Reviewed-on: https://chromium-review.googlesource.com/886651
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: proberge <proberge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532457}
[modify] https://crrev.com/b4de3afbcc0a25e6043ba7c1a2b5ef60101d0694/chrome/browser/ui/toolbar/toolbar_actions_model_unittest.cc
[modify] https://crrev.com/b4de3afbcc0a25e6043ba7c1a2b5ef60101d0694/chrome/common/extensions/manifest_handlers/extension_action_handler.cc

Your change meets the bar and is auto-approved for M65. Please go ahead and merge the CL to branch 3325 manually. Please contact milestone owner if you have questions.
Owners: cmasso@(Android), cmasso@(iOS), bhthompson@(ChromeOS), govind@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Pls merge your change to M65 branch 3325 before 2:00 PM PT tomorrow, Wednesday (02/07/18). Thank you.

Will do. Thank you @govind.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6b7297fa4e7e916f1059b877d924e9b769c23c10

commit 6b7297fa4e7e916f1059b877d924e9b769c23c10
Author: proberge <proberge@chromium.org>
Date: Tue Feb 06 22:24:51 2018

Make ExtensionActionHandler manifest handler parse userscript extensions

This effectively makes user script extensions show up in the tab bar.

(Merging into M65)

Bug:  801861 
Change-Id: I8fd4df034eee07403cda0a0eabef2d68ff5f272a
Reviewed-on: https://chromium-review.googlesource.com/886651
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: proberge <proberge@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#532457}(cherry picked from commit b4de3afbcc0a25e6043ba7c1a2b5ef60101d0694)
Reviewed-on: https://chromium-review.googlesource.com/905580
Reviewed-by: proberge <proberge@chromium.org>
Cr-Commit-Position: refs/branch-heads/3325@{#353}
Cr-Branched-From: bc084a8b5afa3744a74927344e304c02ae54189f-refs/heads/master@{#530369}
[modify] https://crrev.com/6b7297fa4e7e916f1059b877d924e9b769c23c10/chrome/browser/ui/toolbar/toolbar_actions_model_unittest.cc
[modify] https://crrev.com/6b7297fa4e7e916f1059b877d924e9b769c23c10/chrome/common/extensions/manifest_handlers/extension_action_handler.cc

This bug has been closed for more than 14 weeks. Removing security view restrictions.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot