Fixed a problem with spurious wakeups.

runtime/vm/thread_test.cc

Index: runtime/vm/thread_test.cc
diff --git a/runtime/vm/thread_test.cc b/runtime/vm/thread_test.cc
index e8dd4dc9ca0d8eb78bec64c303e05e32957c0f64..22951ccfef11a34e166ea6f640cc2f3f536b98b4 100644
--- a/runtime/vm/thread_test.cc
+++ b/runtime/vm/thread_test.cc
@@ -45,6 +45,7 @@ UNIT_TEST_CASE(Monitor) {
     int64_t wait_time = 2017;
     Monitor::WaitResult wait_result = ml.Wait(wait_time);
     int64_t stop = OS::GetCurrentTimeMillis();
+    // Note: This may fail due to spurious wakeups in pthread_cond_wait().
     EXPECT_EQ(Monitor::kTimedOut, wait_result);
     const int kAcceptableTimeJitter = 20;  // Measured in milliseconds.
     EXPECT_LE(wait_time - kAcceptableTimeJitter, stop - start);