Wait on the monotonic clock to guard against changes to the system clock.

runtime/vm/globals.h

Index: runtime/vm/globals.h
diff --git a/runtime/vm/globals.h b/runtime/vm/globals.h
index d2cb08398b779a1e9e557a5fcca20bfa8f06bf9e..9dfad15ba2ec99575fa5598599e22703f2dc26ad 100644
--- a/runtime/vm/globals.h
+++ b/runtime/vm/globals.h
@@ -158,6 +158,17 @@ const int KB = 1024;
 const int MB = KB * KB;
 const int GB = KB * KB * KB;
 
+// Time constants.
+const int kMillisecondsPerSecond = 1000;
+const int kMicrosecondsPerMillisecond = 1000;
+const int kMicrosecondsPerSecond = (kMicrosecondsPerMillisecond *
+                                    kMillisecondsPerSecond);
+const int kNanosecondsPerMicrosecond = 1000;
+const int kNanosecondsPerMillisecond = (kNanosecondsPerMicrosecond *
+                                        kMicrosecondsPerMillisecond);
+const int kNanosecondsPerSecond = (kNanosecondsPerMicrosecond *
+                                   kMicrosecondsPerSecond);
+
 // A macro to disallow the copy constructor and operator= functions.
 // This should be used in the private: declarations for a class.
 #define DISALLOW_COPY_AND_ASSIGN(TypeName)                                     \