Move SampleStatsCounter to public API

Bug: None
Change-Id: I8956f6febbb1caf71e951d212d57746fe1ec5eb2
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/184506
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32142}
diff --git a/rtc_base/numerics/running_statistics.h b/rtc_base/numerics/running_statistics.h
index 4a3516d..bbcc7e2 100644
--- a/rtc_base/numerics/running_statistics.h
+++ b/rtc_base/numerics/running_statistics.h
@@ -8,8 +8,8 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef RTC_BASE_NUMERICS_RUNNING_STATISTICS_H_
-#define RTC_BASE_NUMERICS_RUNNING_STATISTICS_H_
+#ifndef API_NUMERICS_RUNNING_STATISTICS_H_
+#define API_NUMERICS_RUNNING_STATISTICS_H_
 
 #include <algorithm>
 #include <cmath>
@@ -20,6 +20,7 @@
 #include "rtc_base/numerics/math_utils.h"
 
 namespace webrtc {
+namespace webrtc_impl {
 
 // tl;dr: Robust and efficient online computation of statistics,
 //        using Welford's method for variance. [1]
@@ -154,6 +155,7 @@
   double cumul_ = 0;  // Variance * size_, sometimes noted m2.
 };
 
+}  // namespace webrtc_impl
 }  // namespace webrtc
 
-#endif  // RTC_BASE_NUMERICS_RUNNING_STATISTICS_H_
+#endif  // API_NUMERICS_RUNNING_STATISTICS_H_