This CL adds the API to enable message lifecycle events to be generated.
Those can in turn be used to generate metrics, e.g. latency metrics
tracking the time to send a message, the time until it's acknowledged,
and metrics tracking how often messages are expired.
This will be used to validate that message interleaving really improves
latency for high priority data channels.
The actual implementation of the API will be provided in follow-up CLs.
Bug: webrtc:5696
Change-Id: Ic06f8244d1c79a336975e35479130521dff17519
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/264141
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Victor Boivie <boivie@webrtc.org>
Reviewed-by: Florent Castelli <orphis@webrtc.org>
Commit-Queue: Victor Boivie <boivie@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37396}
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