Fix Mac gen_snapshot by calling TimerUtils::InitOnce

runtime/bin/embedded_dart_io.cc

Index: runtime/bin/embedded_dart_io.cc
diff --git a/runtime/bin/embedded_dart_io.cc b/runtime/bin/embedded_dart_io.cc
index 1b3f40b951d67ef4acc9e8fce6c084255261fc4b..9e38f028734a818ec3c0f6133f54d44162746cc9 100644
--- a/runtime/bin/embedded_dart_io.cc
+++ b/runtime/bin/embedded_dart_io.cc
@@ -5,6 +5,7 @@
 #include "bin/embedded_dart_io.h"
 
 #include "bin/eventhandler.h"
+#include "bin/utils.h"
 #include "bin/thread.h"
 
 namespace dart {
@@ -13,6 +14,7 @@ namespace bin {
 void BootstrapDartIo() {
   // Bootstrap 'dart:io' event handler.
   Thread::InitOnce();
+  TimerUtils::InitOnce();
   EventHandler::Start();
 }