Add missing RTC_GUARDED_BY for ModuleRtpRtcpImpl::rtt_ms_

Bug: None
Change-Id: I7aef516e4310a7ff14a8bbc77c6edd488167d18d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/195338
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32711}

modules/rtp_rtcp/source/rtp_rtcp_impl.h

diff --git a/modules/rtp_rtcp/source/rtp_rtcp_impl.h b/modules/rtp_rtcp/source/rtp_rtcp_impl.h
index 8243076..e04988e 100644
--- a/modules/rtp_rtcp/source/rtp_rtcp_impl.h
+++ b/modules/rtp_rtcp/source/rtp_rtcp_impl.h
@@ -350,7 +350,7 @@
 
   // The processed RTT from RtcpRttStats.
   mutable Mutex mutex_rtt_;
-  int64_t rtt_ms_;
+  int64_t rtt_ms_ RTC_GUARDED_BY(mutex_rtt_);
 };
 
 }  // namespace webrtc

modules/rtp_rtcp/source/rtp_rtcp_impl2.h

diff --git a/modules/rtp_rtcp/source/rtp_rtcp_impl2.h b/modules/rtp_rtcp/source/rtp_rtcp_impl2.h
index 512dfa0..1dde49d8 100644
--- a/modules/rtp_rtcp/source/rtp_rtcp_impl2.h
+++ b/modules/rtp_rtcp/source/rtp_rtcp_impl2.h
@@ -319,7 +319,7 @@
 
   // The processed RTT from RtcpRttStats.
   mutable Mutex mutex_rtt_;
-  int64_t rtt_ms_;
+  int64_t rtt_ms_ RTC_GUARDED_BY(mutex_rtt_);
 };
 
 }  // namespace webrtc