Make HasDataToSend not mutate any state, and let the Produce method do
all state mutation and possibly indicate if there is nothing that can be
sent. This is helpful preparation for extracting the scheduling part of
the send queue to a separate component.
Bug: webrtc:5696
Change-Id: I132779e77d3ce6a41e5fcf4432140d3728d03cdc
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/261945
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Victor Boivie <boivie@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37141}
0e230fd022