Move HistogramPercentileCounter to rtc_base from RecieveStatisticProxy.

This should be a separate utility class, rather than internal thing in
ReceiveStatisticsProxy.

Bug: webrtc:8347
Change-Id: I9c8238e625999dba5776d6038c819732d07e9656
Reviewed-on: https://webrtc-review.googlesource.com/7609
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20267}
diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index 8d93870..0646fb3 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -137,6 +137,8 @@
     "flags.h",
     "format_macros.h",
     "function_view.h",
+    "histogram_percentile_counter.cc",
+    "histogram_percentile_counter.h",
     "ignore_wundef.h",
     "location.cc",
     "location.h",
@@ -895,6 +897,7 @@
       "event_unittest.cc",
       "file_unittest.cc",
       "function_view_unittest.cc",
+      "histogram_percentile_counter_unittest.cc",
       "logging_unittest.cc",
       "md5digest_unittest.cc",
       "mod_ops_unittest.cc",