Add AbsoluteCaptureTime to RtpPacketInfo.

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}

api/rtp_headers.h

@@ -79,6 +79,18 @@ struct AbsoluteCaptureTime {
   absl::optional<int64_t> estimated_capture_clock_offset;
 };
 
+inline bool operator==(const AbsoluteCaptureTime& lhs,
+                       const AbsoluteCaptureTime& rhs) {
+  return (lhs.absolute_capture_timestamp == rhs.absolute_capture_timestamp) &&
+         (lhs.estimated_capture_clock_offset ==
+          rhs.estimated_capture_clock_offset);
+}
+
+inline bool operator!=(const AbsoluteCaptureTime& lhs,
+                       const AbsoluteCaptureTime& rhs) {
+  return !(lhs == rhs);
+}
+
 struct RTPHeaderExtension {
   RTPHeaderExtension();
   RTPHeaderExtension(const RTPHeaderExtension& other);