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In particular, migrate SocketsTcpApiTest.SocketTcpExtension,
SocketsTcpApiTest.SocketTcpExtensionTLS, and
SocketApiTest.SocketTCPExtension.

The second test was using SpawnedTestServer in HTTPS mode, which
could be directly replaced with EmbeddedTestServer in HTTPS mode.
The other two uses the SpawnedTestServer in TCP echo mode. Rather
than write a TCP echo server in C++, this CL switches them over
to use the EmbeddedTestServer in HTTP mode, matching the TLS socket
API test.

The reason for migrating tests off of SpawnedTestServer is that
it has been a source of flaky failures and timeouts for years,
so everything that can use the EmbeddedTestServer or other in-process
C++ servers should be doing so.

Bug: 492672
Change-Id: I655a77abc5a552f6a4edc5edfe3302abdf67fd7c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2513568Reviewed-by: Reilly Grant <reillyg@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823304}