Update thread annotiation macros to use RTC_ prefix

webrtc/call/bitrate_estimator_tests.cc

Index: webrtc/call/bitrate_estimator_tests.cc
diff --git a/webrtc/call/bitrate_estimator_tests.cc b/webrtc/call/bitrate_estimator_tests.cc
index 5d4acbb76ad660d8656467f6569e468a4f7410af..49f149bf0a85b952d3d6fa8a199e8bc6b186a6c2 100644
--- a/webrtc/call/bitrate_estimator_tests.cc
+++ b/webrtc/call/bitrate_estimator_tests.cc
@@ -83,8 +83,8 @@ class LogObserver {
    private:
     typedef std::list<std::string> Strings;
     rtc::CriticalSection crit_sect_;
-    Strings received_log_lines_ GUARDED_BY(crit_sect_);
-    Strings expected_log_lines_ GUARDED_BY(crit_sect_);
+    Strings received_log_lines_ RTC_GUARDED_BY(crit_sect_);
+    Strings expected_log_lines_ RTC_GUARDED_BY(crit_sect_);
     rtc::Event done_;
   };