assigning to jam@ based on https://chromium-review.googlesource.com/912614, which is in the suspected revision range.

and this snippet from the logs:

../../chrome/browser/net/errorpage_browsertest.cc:1257: Failure
Expected equality of these values:
  kRequestsToFail + 1
    Which is: 3
  interceptor_requests()
    Which is: 4

don't know if it's related to your change, but URL.*Intercept seems fairly similar to what's failing.

thanks!

 Issue 811522  has been merged into this issue.

fix out for review in https://chromium-review.googlesource.com/c/chromium/src/+/914872

Detected 8 new flakes for test/step "ErrorPageAutoReloadTest.AutoReload". To see the actual flakes, please visit https://chromium-try-flakes.appspot.com/all_flake_occurrences?key=ahVzfmNocm9taXVtLXRyeS1mbGFrZXNyLQsSBUZsYWtlIiJFcnJvclBhZ2VBdXRvUmVsb2FkVGVzdC5BdXRvUmVsb2FkDA. This message was posted automatically by the chromium-try-flakes app. Since flakiness is ongoing, the issue was moved back into Sheriff Bug Queue (unless already there).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1c4272a8bac8ac274a031212a11fe3b07aa34fe7

commit 1c4272a8bac8ac274a031212a11fe3b07aa34fe7
Author: John Abd-El-Malek <jam@chromium.org>
Date: Wed Feb 14 00:31:23 2018

Fix flake in ErrorPageAutoReloadTest.AutoReload introdued in r536120.

The interceptor was now sometimes seeing the favicon load. Fix the flake by ignoring the favicon request.

Bug:  811520 
Change-Id: I9eda0167678a330f4638d7f077cd87f7aab87233
Reviewed-on: https://chromium-review.googlesource.com/914872
Commit-Queue: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Doug Turner <dougt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536570}
[modify] https://crrev.com/1c4272a8bac8ac274a031212a11fe3b07aa34fe7/chrome/browser/net/errorpage_browsertest.cc

Findit identified the culprit r536120 with confidence 0.0% in the config "tryserver.chromium.linux / linux_chromium_rel_ng"
based on the flakiness trend:

https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVypQELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCJvY2hyb21pdW0ubGludXgvTGludXggVGVzdHMvNjczNzEvbmV0d29ya19zZXJ2aWNlX2Jyb3dzZXJfdGVzdHMvUlhKeWIzSlFZV2RsUVhWMGIxSmxiRzloWkZSbGMzUXVRWFYwYjFKbGJHOWhaQT09DAsSE01hc3RlckZsYWtlQW5hbHlzaXMYAQw

Automatically posted by the findit-for-me app (https://goo.gl/Ot9f7N).
Flake Analyzer is in alpha version.
Feedback is welcome using component Tools>Test>FindIt>Flakiness !