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This replaces the use of multiple EmbeddedTestServer instances with
reused ports (which can be flaky if the ports become unavailable) with
URLLoaderInterceptor which can simulate the legacy TLS and modern TLS
connections for the same server/cert.

Bug: 1150403,1153702
Change-Id: I909199c91c030648d5e81c32d2a880ca6b8a32c8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2601716
Auto-Submit: Chris Thompson <cthomp@chromium.org>
Reviewed-by: Emily Stark <estark@chromium.org>
Commit-Queue: Chris Thompson <cthomp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#839133}