Add WebSocketHandshakeReuseConnection to fieldtrial testing config

Enable WebSocketHandshakeReuseConnection in
fieldtrial_testing_config.json so that it gets testing coverage on the
bots before it becomes the default.

BUG=423609

Change-Id: I692aa12c5685d61a47b26aa014d10db7bb91d98a
Reviewed-on: https://chromium-review.googlesource.com/1151182
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580484}
1 file changed