This allows callers to modify an encoded video frame's SSRC via the setMetadata() call, which we'd like to do from Chrome, to allow using an encoded frame from one PC on a different one. Bug: webrtc:14709 Change-Id: Ia6b33761a3f63038f6eabbcd848916877e24454b Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/292380 Auto-Submit: Tony Herre <herre@google.com> Reviewed-by: Harald Alvestrand <hta@webrtc.org> Commit-Queue: Harald Alvestrand <hta@webrtc.org> Cr-Commit-Position: refs/heads/main@{#39266}