Fix Mac gen_snapshot by calling TimerUtils::InitOnce

runtime/bin/gen_snapshot.cc

Index: runtime/bin/gen_snapshot.cc
diff --git a/runtime/bin/gen_snapshot.cc b/runtime/bin/gen_snapshot.cc
index 773c0af14326a47400f5a7c5af15d5c0433e6b91..93611a4ce93cde33d73e5f30595528c14b2ad11a 100644
--- a/runtime/bin/gen_snapshot.cc
+++ b/runtime/bin/gen_snapshot.cc
@@ -19,6 +19,7 @@
 #include "bin/file.h"
 #include "bin/log.h"
 #include "bin/thread.h"
+#include "bin/utils.h"
 #include "bin/vmservice_impl.h"
 
 #include "platform/globals.h"
@@ -1017,6 +1018,7 @@ int main(int argc, char** argv) {
   Thread::InitOnce();
   DartUtils::SetOriginalWorkingDirectory();
   // Start event handler.
+  TimerUtils::InitOnce();
   EventHandler::Start();
 
   vm_options.AddArgument("--load_deferred_eagerly");