Add Some Comments to the Timeout Checks on Condition Variables

base/synchronization/condition_variable_posix.cc

Index: base/synchronization/condition_variable_posix.cc
diff --git a/base/synchronization/condition_variable_posix.cc b/base/synchronization/condition_variable_posix.cc
index d86fd180ec7f3056dbf22cf0997826b04d7fdde3..d07c67181030752b31dbfe9f0e24571e587bcb92 100644
--- a/base/synchronization/condition_variable_posix.cc
+++ b/base/synchronization/condition_variable_posix.cc
@@ -118,6 +118,8 @@ void ConditionVariable::TimedWait(const TimeDelta& max_time) {
 #endif  // OS_ANDROID && HAVE_PTHREAD_COND_TIMEDWAIT_MONOTONIC
 #endif  // OS_MACOSX
 
+  // On failure, we only expect the CV to timeout. Any other error value means
+  // that we've unexpectedly woken up.
   DCHECK(rv == 0 || rv == ETIMEDOUT);
 #if DCHECK_IS_ON()
   user_lock_->CheckUnheldAndMark();