Why would we need to serve the root?

sperigo, let me know if you're interested in picking this up, and I can give more detail. It would basically just be adding a parameter to this method: https://cs.chromium.org/chromium/src/chrome/browser/ui/webui/interstitials/interstitial_ui.cc?l=129

Re: comment #1: the logic to trigger the interstitial looks for the presence of the root certificate and triggers the interstitial if it's there, so it doesn't trigger on superfish.badssl.com right now unless you actually have the root installed.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9da8b8189b5a1de18665ca383658da498dd1796a

commit 9da8b8189b5a1de18665ca383658da498dd1796a
Author: estark <estark@chromium.org>
Date: Wed Jun 28 20:33:50 2017

Add Superfish interstitial to chrome://interstitials

BUG= 736166 
TEST=Visit chrome://interstitials and click the "Superfish" link

Review-Url: https://codereview.chromium.org/2961013004
Cr-Commit-Position: refs/heads/master@{#483119}

[modify] https://crrev.com/9da8b8189b5a1de18665ca383658da498dd1796a/chrome/browser/ui/webui/interstitials/interstitial_ui.cc
[modify] https://crrev.com/9da8b8189b5a1de18665ca383658da498dd1796a/chrome/browser/ui/webui/interstitials/interstitial_ui_browsertest.cc
[modify] https://crrev.com/9da8b8189b5a1de18665ca383658da498dd1796a/components/security_interstitials/core/browser/resources/list_of_interstitials.html