Update thread annotiation macros to use RTC_ prefix

webrtc/media/base/videocapturer.h

Index: webrtc/media/base/videocapturer.h
diff --git a/webrtc/media/base/videocapturer.h b/webrtc/media/base/videocapturer.h
index a65d40e5ef05537e077fc8a6eed7d86a4affdc0d..10c5df9e3eaf433ed4eb9a53b8b807ebd596fb60 100644
--- a/webrtc/media/base/videocapturer.h
+++ b/webrtc/media/base/videocapturer.h
@@ -271,9 +271,9 @@ class VideoCapturer : public sigslot::has_slots<>,
 
   rtc::CriticalSection frame_stats_crit_;
   // The captured frame size before potential adapation.
-  bool input_size_valid_ GUARDED_BY(frame_stats_crit_) = false;
-  int input_width_ GUARDED_BY(frame_stats_crit_);
-  int input_height_ GUARDED_BY(frame_stats_crit_);
+  bool input_size_valid_ RTC_GUARDED_BY(frame_stats_crit_) = false;
+  int input_width_ RTC_GUARDED_BY(frame_stats_crit_);
+  int input_height_ RTC_GUARDED_BY(frame_stats_crit_);
 
   // Whether capturer should apply rotation to the frame before
   // passing it on to the registered sinks.