Update thread annotiation macros to use RTC_ prefix

BUG=webrtc:8198

Review-Url: https://codereview.webrtc.org/3012853002
Cr-Commit-Position: refs/heads/master@{#19760}
diff --git a/webrtc/call/bitrate_estimator_tests.cc b/webrtc/call/bitrate_estimator_tests.cc
index 5d4acbb..49f149b 100644
--- a/webrtc/call/bitrate_estimator_tests.cc
+++ b/webrtc/call/bitrate_estimator_tests.cc
@@ -83,8 +83,8 @@
    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_;
   };