Manual bisect points to https://crrev.com/c/927491.

https://crrev.com/c/927491 only touched websocket_stream_test.cc.  There are 51 tests in that file.  For each of these (including SelfSignedCertificateFailure and SelfSignedCertificateSuccess themselves), I ran a net_unittest command running exactly two tests: that one first, and each of SelfSignedCertificateFailure and SelfSignedCertificateSuccess second.  This is 102 runs of net_unittest, each with exactly two tests.

For the following 4 tests, both SelfSignedCertificate* tests fail when run right after:
WebSocketStreamCreateTest.Cancellation
WebSocketStreamCreateTest.HandshakeTimeout
WebSocketStreamCreateTest.CancellationDuringConnect
WebSocketStreamCreateTest.NeedsToRunLoop

For the other tests, there are no failures.

I am reverting https://crrev.com/c/927491 for the time being (to make sure that CLs introducing new tests to the existing ~30000 net_unittests will not rearrange the sharding-by-10 triggering this issue, and also to make sure that developers can run tests with --single-process-tests locally).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6c7c2520da894d75c518262a9281a8b4c4791cfa

commit 6c7c2520da894d75c518262a9281a8b4c4791cfa
Author: Bence Béky <bnc@chromium.org>
Date: Fri Feb 23 16:04:15 2018

Revert "Change most WebSocketStreamCreate*Tests to use wss scheme."

This reverts commit ed718f52c14b7678c6b1fbce8bb0c86375bbef60.

Reason for revert:  https://crbug.com/814982 

Original change's description:
> Change most WebSocketStreamCreate*Tests to use wss scheme.
>
> Most of these tests will be adopted to test WebSockets over HTTP/2 as
> well, but that only works with wss.  Also, change hosts and origins from
> localhost to www.example.org instead so that it works with the test
> certificate.
>
> Also, change WebSocketStreamCreateUMATest to be a derived class of
> WebSocketStreamCreateTest instead of creating an instance of it.  This
> will also help with turning this into a parametrized class.
>
> Bug: 801564
> Change-Id: Ifff2262bcc15e0ee6ab67dea10cef605d47bd907
> Reviewed-on: https://chromium-review.googlesource.com/927491
> Reviewed-by: Adam Rice <ricea@chromium.org>
> Commit-Queue: Bence Béky <bnc@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#538081}

TBR=ricea@chromium.org,bnc@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 801564,  814982 
Change-Id: I27a752f3100d72087ca4ec436d8758915e71e4ec
Reviewed-on: https://chromium-review.googlesource.com/934601
Commit-Queue: Bence Béky <bnc@chromium.org>
Reviewed-by: Bence Béky <bnc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#538790}
[modify] https://crrev.com/6c7c2520da894d75c518262a9281a8b4c4791cfa/net/websockets/websocket_stream_test.cc