Move smoothing filter to common audio and exp_filter to base/analytics.

webrtc/base/BUILD.gn

Index: webrtc/base/BUILD.gn
diff --git a/webrtc/base/BUILD.gn b/webrtc/base/BUILD.gn
index d1e600288b3c1849f0d534c4e87e9405ba9c390e..71f9ec45e4c4206fb417d60ead6bde29bc974149 100644
--- a/webrtc/base/BUILD.gn
+++ b/webrtc/base/BUILD.gn
@@ -124,8 +124,6 @@ rtc_static_library("rtc_base_approved") {
     "event.h",
     "event_tracer.cc",
     "event_tracer.h",
-    "exp_filter.cc",
-    "exp_filter.h",
     "file.cc",
     "file.h",
     "format_macros.h",
@@ -338,6 +336,13 @@ rtc_static_library("rtc_task_queue") {
   }
 }
 
+rtc_static_library("rtc_analytics") {
+  sources = [
+    "analytics/exp_filter.cc",
+    "analytics/exp_filter.h",
+  ]
+}
+
 config("rtc_base_warnings_config") {
   if (is_win && is_clang) {
     cflags = [