Thanks for filing the issue!

Unable top reproduce the issue on reported chrome version 66.0.3354.0 using windows 10 with the below mentioned steps.
1. Launched Chrome 
2. Enabled the flag mentioned in comment#0 and relaunched chrome
3. Navigated to http://www.chromium.org
4. Opened DevTools -> Security
We didn't observe any text like "This page is not secure (broken HTTPS)". Attaching the screen shot of the same.

@Reporter: Could you please have a look at the screen shot and let us know if anything missed from our end. Any further inputs from your end may help us.

Deleted: 816184.png 44.1 KB

	816184.png 44.1 KB View Download

Can you provide a full screenshot with the browser chrome as well, so that I can confirm that the flag is actually enabled?

Thank you for providing more feedback. Adding the requester to the cc list.

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

93m4qau783 Thanks for the feedback.

As per comment #3, attached is the screen shot with the chrome//version showing the flag #enable-mark-http-as Enabled.

Request you to please check and confirm if anything is missed from our end, which will help in further triaging.

Thanks..

Deleted: 816184.png 149 KB

	816184.png 149 KB View Download

You may need to set the flag to "Always mark HTTP as actively dangerous", so you get a red "Not secure" next to the URL.

Thank you for providing more feedback. Adding the requester to the cc list.

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

Able to reproduce this issue on Mac 10.13.3, Win-10 and Ubuntu 14.04 using chrome reported version #66.0.3354.0 and latest canary #67.0.3362.0.
This is a non-regression issue as it is observed from M65 old builds i.e the flag got introduced in M-65 only. 

Hence, marking it as untriaged to get more inputs from dev team.

Thanks...!!

Sorry, wrong triage. Emily, mind taking a look?

 Issue 882202  has been merged into this issue.

see  issue 882202  for further repro steps. Assigning to cthomp as estark is away.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/addf5286b849bdcc235e63e170c948f60cf8892c

commit addf5286b849bdcc235e63e170c948f60cf8892c
Author: Christopher Thompson <cthomp@chromium.org>
Date: Mon Oct 29 22:28:01 2018

Add security summary override for HTTP-Really-Bad

This adds a new summary and sets the explanation for non-secure form
edits on HTTP pages in the DevTools security panel. This fixes a bug
where HTTP pages downgraded to the DANGEROUS security level (under the
HTTP-Really-Bad changes) would get treated as broken HTTPS instead.

Bug:  816184 
Change-Id: I9440a20f970ff4daffd9c3a11a6a5a86a0b39160
Reviewed-on: https://chromium-review.googlesource.com/c/1277650
Reviewed-by: Adrienne Porter Felt <felt@chromium.org>
Commit-Queue: Christopher Thompson <cthomp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603657}
[modify] https://crrev.com/addf5286b849bdcc235e63e170c948f60cf8892c/components/security_state/content/content_utils.cc
[modify] https://crrev.com/addf5286b849bdcc235e63e170c948f60cf8892c/components/security_state/content/content_utils_unittest.cc
[modify] https://crrev.com/addf5286b849bdcc235e63e170c948f60cf8892c/components/security_state_strings.grdp

Marking this as fixed as I don't think there is anything remaining to do.