HttpStreamPool: Add stream count consistency check

This CL adds stream counts consistency check for debugging. When the
"enable_consistency_check" feature param is enabled for the
HappyEyeballsV3 feature, we periodically run a task that checks
stream count consistency among the pool and groups. The task logs
results to NetLog and/or VLOG.

Bug: 346835898
Change-Id: Ic68ce24c2d53f9a47d1ab29f21d725ec59522ca3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5933451
Reviewed-by: Nidhi Jaju <nidhijaju@chromium.org>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1369780}