Have --print-metrics use stderr to work around issue with analyzer_cli

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
diff --git a/runtime/vm/isolate.cc b/runtime/vm/isolate.cc
index 5dc9a9f6b4807f08f4723738baa3015ba23522fe..72d7b91ba124979af3dc74dfafd9291b96f4de0a 100644
--- a/runtime/vm/isolate.cc
+++ b/runtime/vm/isolate.cc
@@ -1630,13 +1630,13 @@ void Isolate::LowLevelShutdown() {
   }
   if (FLAG_print_metrics) {
     LogBlock lb;
-    THR_Print("Printing metrics for %s\n", name());
+    OS::PrintErr("Printing metrics for %s\n", name());
 #define ISOLATE_METRIC_PRINT(type, variable, name, unit)                       \
-  THR_Print("%s\n", metric_##variable##_.ToString());
+  OS::PrintErr("%s\n", metric_##variable##_.ToString());
 
     ISOLATE_METRIC_LIST(ISOLATE_METRIC_PRINT);
 #undef ISOLATE_METRIC_PRINT
-    THR_Print("\n");
+    OS::PrintErr("\n");
   }
 }