Introduce Metric object for new perf metrics logging system

Bug: b/246095034
Change-Id: I854ee8e5ea93e4046837ae9f54a652a8c92dd1bc
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/274861
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#38078}
diff --git a/BUILD.gn b/BUILD.gn
index 92941f0..4146db8 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -52,6 +52,7 @@
         ":voip_unittests",
         ":webrtc_nonparallel_tests",
         ":webrtc_perf_tests",
+        "api/test/metrics:metrics_unittests",
         "common_audio:common_audio_unittests",
         "common_video:common_video_unittests",
         "examples:examples_unittests",
@@ -475,6 +476,7 @@
       "api/rtc_event_log:rtc_event_log_factory",
       "api/task_queue",
       "api/task_queue:default_task_queue_factory",
+      "api/test/metrics",
       "audio",
       "call",
       "common_audio",