Reland "stats: migrate to Timestamp"

This is a reland of commit 2235776597e2f47ec353ac911428eb9a54d64a10

Original change's description:
> stats: migrate to Timestamp
>
> BUG=webrtc:13756
>
> Change-Id: I04ba57f9c2ca5a974a406814023911b4eb2d6d38
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/273942
> Commit-Queue: Philipp Hancke <phancke@microsoft.com>
> Reviewed-by: Henrik Boström <hbos@webrtc.org>
> Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
> Cr-Commit-Position: refs/heads/main@{#38365}

Bug: webrtc:13756
Change-Id: Ib8dc208197ae5e90f67114e7b043a73ee35421ea
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/279080
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@microsoft.com>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#38380}
diff --git a/pc/rtc_stats_traversal_unittest.cc b/pc/rtc_stats_traversal_unittest.cc
index 6e9b784..efc7bbc 100644
--- a/pc/rtc_stats_traversal_unittest.cc
+++ b/pc/rtc_stats_traversal_unittest.cc
@@ -28,14 +28,14 @@
     candidate_pair_ = new RTCIceCandidatePairStats("candidate-pair", 0);
     local_candidate_ = new RTCLocalIceCandidateStats("local-candidate", 0);
     remote_candidate_ = new RTCRemoteIceCandidateStats("remote-candidate", 0);
-    initial_report_ = RTCStatsReport::Create(0);
+    initial_report_ = RTCStatsReport::Create(Timestamp::Zero());
     initial_report_->AddStats(std::unique_ptr<const RTCStats>(transport_));
     initial_report_->AddStats(std::unique_ptr<const RTCStats>(candidate_pair_));
     initial_report_->AddStats(
         std::unique_ptr<const RTCStats>(local_candidate_));
     initial_report_->AddStats(
         std::unique_ptr<const RTCStats>(remote_candidate_));
-    result_ = RTCStatsReport::Create(0);
+    result_ = RTCStatsReport::Create(Timestamp::Zero());
   }
 
   void TakeReferencedStats(std::vector<const RTCStats*> start_nodes) {