danilchap@webrtc.org suggested to add a converter for NtpTime <-> UTC Timestamp for in https://webrtc-review.googlesource.com/c/src/+/365641. This CL add a NtpTime -> UTC Timestamp in Clock, and change code to start to use the new function. Bug: None Change-Id: If4af6cb8e31c1731692edfb8358e67b7a43226a0 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/366001 Commit-Queue: Olov Brändström <brandstrom@google.com> Reviewed-by: Henrik Boström <hbos@webrtc.org> Reviewed-by: Danil Chapovalov <danilchap@webrtc.org> Reviewed-by: Henrik Andreassson <henrika@webrtc.org> Cr-Commit-Position: refs/heads/main@{#43293}