Move SampleCounter from ReceiveStatisticsProxy to rtc_base/numerics

This class will be used in upcoming VideoQualiyObserver.

Bug: none
Change-Id: I7d79a6caf3040a3f707ed8700842dea1de81e0a6
Reviewed-on: https://webrtc-review.googlesource.com/77724
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23343}
diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index aaf974e..43172a9 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -417,6 +417,8 @@
     "numerics/histogram_percentile_counter.h",
     "numerics/mod_ops.h",
     "numerics/moving_max_counter.h",
+    "numerics/sample_counter.cc",
+    "numerics/sample_counter.h",
     "onetimeevent.h",
     "pathutils.cc",
     "pathutils.h",
@@ -1140,6 +1142,7 @@
       "numerics/moving_max_counter_unittest.cc",
       "numerics/safe_compare_unittest.cc",
       "numerics/safe_minmax_unittest.cc",
+      "numerics/sample_counter_unittest.cc",
       "onetimeevent_unittest.cc",
       "pathutils_unittest.cc",
       "platform_file_unittest.cc",