This change stores the optional `AbsoluteCaptureTime` header extension in `RtpPacketInfo` so that we later can consume it in `SourceTracker`. Bug: webrtc:10739 Change-Id: I975e8863117fcda134535cd49ad71079a7ff38ec Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/148068 Reviewed-by: Karl Wiberg <kwiberg@webrtc.org> Commit-Queue: Chen Xing <chxg@google.com> Cr-Commit-Position: refs/heads/master@{#28790}