Fix Mac gen_snapshot by calling TimerUtils::InitOnce

runtime/bin/vmservice_dartium.cc

Index: runtime/bin/vmservice_dartium.cc
diff --git a/runtime/bin/vmservice_dartium.cc b/runtime/bin/vmservice_dartium.cc
index aa5a62a654b77a339632eb12fc6e25fc1836780c..0ff30a7b6f2ecdf8ac9a58800a1b4dbba7776f98 100644
--- a/runtime/bin/vmservice_dartium.cc
+++ b/runtime/bin/vmservice_dartium.cc
@@ -9,6 +9,7 @@
 #include "bin/eventhandler.h"
 #include "bin/platform.h"
 #include "bin/thread.h"
+#include "bin/utils.h"
 #include "bin/vmservice_impl.h"
 #include "zlib/zlib.h"
 
@@ -34,6 +35,7 @@ void VmServiceServer::Bootstrap() {
   }
   DartUtils::SetOriginalWorkingDirectory();
   Thread::InitOnce();
+  TimerUtils::InitOnce();
   EventHandler::Start();
 }