Change thread check to race check

webrtc/base/race_checker.cc

Index: webrtc/base/race_checker.cc
diff --git a/webrtc/base/race_checker.cc b/webrtc/base/race_checker.cc
index 9f0946ca76f87e1386219b21f8073676f3497a00..96bb6cce7bb827e64af6991d304edbe5342a12a6 100644
--- a/webrtc/base/race_checker.cc
+++ b/webrtc/base/race_checker.cc
@@ -14,6 +14,12 @@ namespace rtc {
 
 RaceChecker::RaceChecker() {}
 
+// Note that the implementation here is in itself racy, but we pretend it does
+// not matter because we want this useful in release builds without having to
+// pay the cost of using atomics. A race hitting the race checker is likely to
+// cause access_count_ to diverge from zero and therefore cause the ThreadRef
+// comparison to fail, signaling a race, although it may not be in the exact
+// spot where a race *first* appeared in the code we're trying to protect.

[kwiberg-webrtc, 2016/09/22 20:12:17]

Maybe not that it's known that a race may also cause us to fail to detect the
race, or (very unlikely!) eat your dog, but that this is a deliberately chosen
trade-off. Without such a note, we'd still have spent all this time digging
through the code.

 bool RaceChecker::Acquire() const {
   const PlatformThreadRef current_thread = CurrentThreadRef();
   // Set new accessing thread if this is a new use.