Findit identified the culprit r574621 with confidence 70.0% in the config "chromium.win / Win 7 Tests x64 (1)"
based on the flakiness trend:

https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVypwELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCJxY2hyb21pdW0ud2luL1dpbiA3IFRlc3RzIHg2NCAoMSkvNDA3NDQvYnJvd3Nlcl90ZXN0cy9VMU5NVlVsWGIzSnJaWEpHWlhSamFGUmxjM1F1VFdsNFpXUkRiMjUwWlc1MFUzVmlSbkpoYldVdk13PT0MCxITTWFzdGVyRmxha2VBbmFseXNpcxgBDA

If the culprit above is wrong, please file a bug using this link and hit submit:
https://bugs.chromium.org/p/chromium/issues/entry?status=Unconfirmed&labels=Pri-1,Test-Findit-Wrong&components=Tools%3ETest%3EFindit%3EFlakiness&summary=%5BFindit%5D%20Flake%20Analyzer%20-%20Wrong%20result%20for%20SSLUIWorkerFetchTest.MixedContentSubFrame/3&comment=Link%20to%20Analysis%3A%20https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVypwELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCJxY2hyb21pdW0ud2luL1dpbiA3IFRlc3RzIHg2NCAoMSkvNDA3NDQvYnJvd3Nlcl90ZXN0cy9VMU5NVlVsWGIzSnJaWEpHWlhSamFGUmxjM1F1VFdsNFpXUkRiMjUwWlc1MFUzVmlSbkpoYldVdk13PT0MCxITTWFzdGVyRmxha2VBbmFseXNpcxgBDA

Automatically posted by the findit-for-me app (https://goo.gl/Ot9f7N).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d27b4a8038e27c816a16c788a4a749ae7a76ed5e

commit d27b4a8038e27c816a16c788a4a749ae7a76ed5e
Author: Mike West <mkwst@chromium.org>
Date: Fri Jul 13 09:53:38 2018

Revert "Changed committed-interstitials flag from switch to feature."

This reverts commit 49040ae795592d3b0c6a5b03533565caeb9ae266.

Reason for revert: 

Findit (https://goo.gl/kROfz5) identified this CL at revision 574621 as the culprit
for introducing flakiness in the tests as shown on:
https://findit-for-me.appspot.com/waterfall/flake/flake-culprit?key=ag9zfmZpbmRpdC1mb3ItbWVyQwsSDEZsYWtlQ3VscHJpdCIxY2hyb21pdW0vNDkwNDBhZTc5NTU5MmQzYjBjNmE1YjAzNTMzNTY1Y2FlYjlhZTI2Ngw

Original change's description:
> Changed committed-interstitials flag from switch to feature.
> 
> Removed 'committed-interstitials' switch and added SSLCommittedInterstitials
> base::Feature. Name was changed to SSLCommmittedInterstitials since we are now
> doing separate rampups for each kind of committed interstitial. Switch was
> changed to Feature so that it can be enabled via variations.
> 
> Bug: 755632
> Change-Id: I0f3e0e01a94be2b515aa596827cd447d14c24b56
> Reviewed-on: https://chromium-review.googlesource.com/1118975
> Commit-Queue: Carlos IL <carlosil@chromium.org>
> Reviewed-by: Jialiu Lin <jialiul@chromium.org>
> Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
> Reviewed-by: Emily Stark <estark@chromium.org>
> Reviewed-by: Giovanni Ortuño Urquidi <ortuno@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#574621}

TBR=emaxx@chromium.org,estark@chromium.org,ortuno@chromium.org,jialiul@chromium.org,carlosil@chromium.org

Change-Id: If9f9b15c8e3654dbd011104dfa469943bcd66e0c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 755632,  863272 
Reviewed-on: https://chromium-review.googlesource.com/1136351
Reviewed-by: Mike West <mkwst@chromium.org>
Commit-Queue: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574870}
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/browser/about_flags.cc
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/browser/chrome_content_browser_client.cc
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/browser/flag_descriptions.cc
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/browser/flag_descriptions.h
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/browser/policy/policy_browsertest.cc
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/browser/safe_browsing/certificate_reporting_service_browsertest.cc
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/browser/ssl/captive_portal_blocking_page_browsertest.cc
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/browser/ssl/connection_help_tab_helper.cc
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/browser/ssl/connection_help_tab_helper_browsertest.cc
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/browser/ssl/security_state_tab_helper_browsertest.cc
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/browser/ssl/ssl_browsertest.cc
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/browser/ssl/ssl_browsertest_util.cc
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/browser/ssl/ssl_error_controller_client.cc
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/browser/ssl/ssl_error_navigation_throttle.cc
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/browser/ssl/ssl_error_navigation_throttle_unittest.cc
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/browser/ui/extensions/hosted_app_browsertest.cc
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/common/chrome_features.cc
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/common/chrome_features.h
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/common/chrome_switches.cc
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/chrome/common/chrome_switches.h
[modify] https://crrev.com/d27b4a8038e27c816a16c788a4a749ae7a76ed5e/tools/metrics/histograms/enums.xml

 Issue 863275  has been merged into this issue.

 Issue 863349  has been merged into this issue.

 Issue 863406  has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/defd3adc81c981e10862d1851723c5259e65efb2

commit defd3adc81c981e10862d1851723c5259e65efb2
Author: Carlos IL <carlosil@chromium.org>
Date: Wed Aug 22 21:57:18 2018

Re-enabled committed interstitial tests for MixedContentSettings

Couldn't reproduce the flakiness in those tests, so re-enabling with
committed interstitials, will revert this CL if the flakiness returns.
Also: This tests seem to be flaky in general, even without committed
interstitials, e.g., crbug.com/874959

Bug:  863272 
Change-Id: I64b5291513041e4dd9da9fa6125785fe4727a6c7
Reviewed-on: https://chromium-review.googlesource.com/1178928
Commit-Queue: Carlos IL <carlosil@chromium.org>
Reviewed-by: Mustafa Emre Acer <meacer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585270}
[modify] https://crrev.com/defd3adc81c981e10862d1851723c5259e65efb2/chrome/browser/ssl/ssl_browsertest.cc

Re-enabled the test on that CL, and so far Findit hasn't complained, so closing this bug.