tracing: Fix browser crash on socket connection failure on CrOS

The UnixSocket listener for connecting the producer socket on behalf of
child processes crashes when the OnConnect() callback is called but the
connection isn't successful. Releasing the socket will cause a crash
that the FD is released from file descriptor watcher twice. Check
connection status before stealing the socket FD to fix the crash.

Bug: 996777
Test: update services_unittests: SystemTracingService.*
Change-Id: I2eab7473ce9486d20bc79b0aa925027453b4192a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3141450


Reviewed-by: Stephen Nusko <nuskos@chromium.org>
Commit-Queue: Chinglin Yu <chinglinyu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#918763}