Update thread annotiation macros in modules to use RTC_ prefix

webrtc/modules/video_coding/protection_bitrate_calculator.h

Index: webrtc/modules/video_coding/protection_bitrate_calculator.h
diff --git a/webrtc/modules/video_coding/protection_bitrate_calculator.h b/webrtc/modules/video_coding/protection_bitrate_calculator.h
index d2c1499231bd158ca6cb57e6c39490cdbc4a67d0..d6496958c8db0df06f42c3689f86fa38cb26cb51 100644
--- a/webrtc/modules/video_coding/protection_bitrate_calculator.h
+++ b/webrtc/modules/video_coding/protection_bitrate_calculator.h
@@ -69,8 +69,8 @@ class ProtectionBitrateCalculator {
 
   rtc::CriticalSection crit_sect_;
   std::unique_ptr<media_optimization::VCMLossProtectionLogic> loss_prot_logic_
-      GUARDED_BY(crit_sect_);
-  size_t max_payload_size_ GUARDED_BY(crit_sect_);
+      RTC_GUARDED_BY(crit_sect_);
+  size_t max_payload_size_ RTC_GUARDED_BY(crit_sect_);
 
   RTC_DISALLOW_COPY_AND_ASSIGN(ProtectionBitrateCalculator);
 };