Rohit, do you want to take this bug?

I was thinking of taking this.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8ab9f1efc15968efe754949d7606842f62273428

commit 8ab9f1efc15968efe754949d7606842f62273428
Author: Rohit Rao <rohitrao@chromium.org>
Date: Mon Nov 26 18:13:45 2018

Moves user_actions webui resources to components/user_actions_ui.

This will allow the resources to be reused on iOS.

BUG= 903381 

Change-Id: I3f026a8c38da99eab403eb54ab57ad9503f9ddd5
Reviewed-on: https://chromium-review.googlesource.com/c/1332409
Commit-Queue: Rohit Rao <rohitrao@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610890}
[modify] https://crrev.com/8ab9f1efc15968efe754949d7606842f62273428/chrome/browser/browser_resources.grd
[modify] https://crrev.com/8ab9f1efc15968efe754949d7606842f62273428/chrome/browser/ui/webui/user_actions/user_actions_ui.cc
[modify] https://crrev.com/8ab9f1efc15968efe754949d7606842f62273428/components/resources/components_resources.grd
[add] https://crrev.com/8ab9f1efc15968efe754949d7606842f62273428/components/resources/user_actions_ui_resources.grdp
[add] https://crrev.com/8ab9f1efc15968efe754949d7606842f62273428/components/user_actions_ui/OWNERS
[rename] https://crrev.com/8ab9f1efc15968efe754949d7606842f62273428/components/user_actions_ui/resources/user_actions.css
[rename] https://crrev.com/8ab9f1efc15968efe754949d7606842f62273428/components/user_actions_ui/resources/user_actions.html
[rename] https://crrev.com/8ab9f1efc15968efe754949d7606842f62273428/components/user_actions_ui/resources/user_actions.js

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c3178000758efe9625d96e4b9ae2d5a4e9c45a1b

commit c3178000758efe9625d96e4b9ae2d5a4e9c45a1b
Author: Rohit Rao <rohitrao@chromium.org>
Date: Tue Nov 27 14:07:11 2018

[ios] Enables chrome://user-actions.

BUG= 903381 

Change-Id: Ic99dc1e7d52e434a5f2b38b0fa561921aab26065
Reviewed-on: https://chromium-review.googlesource.com/c/1328821
Reviewed-by: Peter Lee <pkl@chromium.org>
Commit-Queue: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611095}
[modify] https://crrev.com/c3178000758efe9625d96e4b9ae2d5a4e9c45a1b/ios/chrome/browser/chrome_url_constants.cc
[modify] https://crrev.com/c3178000758efe9625d96e4b9ae2d5a4e9c45a1b/ios/chrome/browser/chrome_url_constants.h
[modify] https://crrev.com/c3178000758efe9625d96e4b9ae2d5a4e9c45a1b/ios/chrome/browser/ui/webui/BUILD.gn
[modify] https://crrev.com/c3178000758efe9625d96e4b9ae2d5a4e9c45a1b/ios/chrome/browser/ui/webui/chrome_web_ui_ios_controller_factory.mm
[add] https://crrev.com/c3178000758efe9625d96e4b9ae2d5a4e9c45a1b/ios/chrome/browser/ui/webui/user_actions_handler.h
[add] https://crrev.com/c3178000758efe9625d96e4b9ae2d5a4e9c45a1b/ios/chrome/browser/ui/webui/user_actions_handler.mm
[add] https://crrev.com/c3178000758efe9625d96e4b9ae2d5a4e9c45a1b/ios/chrome/browser/ui/webui/user_actions_ui.h
[add] https://crrev.com/c3178000758efe9625d96e4b9ae2d5a4e9c45a1b/ios/chrome/browser/ui/webui/user_actions_ui.mm

Can this be considered "fixed" after c4 and c5 ?

Issue 840654 has been merged into this issue.