Adding missing RTC_EXPORT for component build.

Bug: webrtc:9419
Change-Id: Ifa5d21edc708b5012b71e2e5101e10c6352a7218
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/157162
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29533}
diff --git a/rtc_base/rate_statistics.h b/rtc_base/rate_statistics.h
index a423654..65b5fa1 100644
--- a/rtc_base/rate_statistics.h
+++ b/rtc_base/rate_statistics.h
@@ -17,10 +17,11 @@
 #include <memory>
 
 #include "absl/types/optional.h"
+#include "rtc_base/system/rtc_export.h"
 
 namespace webrtc {
 
-class RateStatistics {
+class RTC_EXPORT RateStatistics {
  public:
   static constexpr float kBpsScale = 8000.0f;