This CL updates H26xPacketBuffer to store and prepend SPS and PPS for H.264 bitstreams when IDR only keyframe is allowed. Bug: webrtc:13485 Change-Id: Ic1edc623dff568d54d3ce29b42dd8eab3312f5cb Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/342225 Reviewed-by: Philip Eliasson <philipel@webrtc.org> Commit-Queue: Philip Eliasson <philipel@webrtc.org> Reviewed-by: Sergey Silkin <ssilkin@webrtc.org> Cr-Commit-Position: refs/heads/main@{#41986}