Eric, could you take this one?

The only tricky part about this is that we probably want to record the histogram at most once per main-frame navigation (like the console message), not every time the toolbar redraws.

We could simply record it inside ChromeSecurityStateModelClient::VisibleSSLStateChanged[1], where we do the console message. That would be a pretty simple approach, but it has the downside that we'd have to do a separate histogram for iOS, since iOS doesn't use ChromeSecurityStateModelClient but instead has its own IOSChromeSecurityStateModelClient.

An alternative would be that we could forward the ChromeSSMClient::VisibleSSLStateChanged and DidFinishNavigation calls on to SecurityStateModel, and record the histogram in SecurityStateModel (which is shared with iOS).

I'd be fine with either approach.

[1] https://cs.chromium.org/chromium/src/chrome/browser/ssl/chrome_security_state_model_client.cc?sq=package:chromium&l=308

https://codereview.chromium.org/2451293002

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c346a85602ff22ead6e8ce22f370267e3f192230

commit c346a85602ff22ead6e8ce22f370267e3f192230
Author: elawrence <elawrence@chromium.org>
Date: Fri Oct 28 18:43:46 2016

Add a histogram for each time the HTTP Bad UI is shown

Log a sample each time a HTTP Bad UI warning is shown in either the console or
the omnibox.

BUG= 647567 

Review-Url: https://codereview.chromium.org/2451293002
Cr-Commit-Position: refs/heads/master@{#428441}

[modify] https://crrev.com/c346a85602ff22ead6e8ce22f370267e3f192230/chrome/browser/ssl/chrome_security_state_model_client.cc
[modify] https://crrev.com/c346a85602ff22ead6e8ce22f370267e3f192230/chrome/browser/ssl/chrome_security_state_model_client_unittest.cc
[modify] https://crrev.com/c346a85602ff22ead6e8ce22f370267e3f192230/tools/metrics/histograms/histograms.xml

Eric, could you add a link to where I'd go to see this metric?