Fix NetworkMonitor race condition when dispatching native observers

There is a race condition in NetworkMonitor where native observers may be removed concurrently with a notification being dispatched, leading to a dangling pointer dereference (trying to dispatch an observer that was already removed and destroyed), and from there a crash with access violation.

By ensuring dispatching to native observers is done within the synchronization lock that guards additions/removals of native observers protects against this race condition. Since native observers callbacks are posted to the networking thread in the C++ side anyway, there should be no risk of deadlock/starvation due to long-running observers.

Bug: webrtc:15837 Change-Id: Id2b788f102dbd25de76ceed434c4cd68aa9a569e Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/338643 Reviewed-by: Taylor Brandstetter deadbeef@webrtc.org Commit-Queue: Harald Alvestrand hta@webrtc.org Reviewed-by: Harald Alvestrand hta@webrtc.org Cr-Commit-Position: refs/heads/main@{#42256}

webrtc-sdk / webrtc

Fix NetworkMonitor race condition when dispatching native observers #135