Add MovingMedianFilter to rtc_base/numerics

This class will be used for filtering remote clock offset in rtp streams.
It is a separate wrapper around PercentileFilter because it will be used
in that form in several places.

Bug: webrtc:8468
Change-Id: If1f6c38ac1ffa02232c1aed5512b92878b1c346a
Reviewed-on: https://webrtc-review.googlesource.com/17841
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Tommi <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20531}
diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index 775fd14..400efb6 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -402,6 +402,7 @@
   sources = [
     "numerics/exp_filter.cc",
     "numerics/exp_filter.h",
+    "numerics/moving_median_filter.h",
     "numerics/percentile_filter.h",
     "numerics/sequence_number_util.h",
   ]
@@ -997,6 +998,7 @@
     }
     sources = [
       "numerics/exp_filter_unittest.cc",
+      "numerics/moving_median_filter_unittest.cc",
       "numerics/percentile_filter_unittest.cc",
       "numerics/sequence_number_util_unittest.cc",
     ]