If it's possible to make available, please make chrome://user-actions available at well.

(It uses the same mechanisms--a WebUI page that uses Javascript to receive Mojo messages--so if one can work, the other can work as well.)

Once you figure out what is available / can be available, this also might be a good time to consider enabling built-in provider on iOS.  (This is the provider that suggests completions of partially-typed chrome:// URLs.)

"It uses the same mechanisms--a WebUI page that uses Javascript to receive Mojo messages"

Ah, this most likely explains the absence of this feature, then. Mojo messaging in not available on iOS. The communication to the Javascript will likely require custom plumbing.

I originally wrote chrome://omnibox using a pre-mojo message passing method.  If you look into the history of the code, perhaps you can check to see if the older version would work on iOS?

Eugene tells me that mojo messaging works on iOS for webui pages.  Can we look specifically at what is needed for this page to see if it's supported or not?

We don't have any pages on iOS that use Mojo, however all JS bindings API should work (tests confirm that). This is iOS CL which adds Mojo support for chrome://version:
https://codereview.chromium.org/2041603002/ and it can be used as an example.

Removing myself as owner of this issue as there's no chance I'll do this, however I still believe that this would be valuable.

+rkgibson@google.com who may be interested given his recent work on the omnibox

+manuk FYI as chrome://omnibox owner