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The test is trying to verify that WebEngine closes devtools port as
expected. It was using URLFetcher to make an HTTP request to devtools.
Due to a netstack bug (fxb/49779) sometimes that request was hanging
indefinitely, so the test was timing out. Updated the tests to connect
raw socket, which allows to verify that the port is closed without
hitting that netstack bug.

Bug: 1067727
Change-Id: Id07eefe490ca4e25cf6d9143636802f8115cd0db
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2143380Reviewed-by: Fabrice de Gans-Riberi <fdegans@chromium.org>
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Auto-Submit: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#757920}