Gardening: mark tests that are timing out as slow

runtime/vm/scopes.cc

Index: runtime/vm/scopes.cc
diff --git a/runtime/vm/scopes.cc b/runtime/vm/scopes.cc
index e7c04323367039040209ec798b4ba7870dddae1e..277935bf818100250aba2d9c392e1ad177265982 100644
--- a/runtime/vm/scopes.cc
+++ b/runtime/vm/scopes.cc
@@ -639,7 +639,8 @@ void LocalScope::CaptureLocalVariables(LocalScope* top_scope) {
       if (variable->is_forced_stack() ||
           (variable->name().raw() == Symbols::StackTraceVar().raw()) ||
           (variable->name().raw() == Symbols::ExceptionVar().raw()) ||
-          (variable->name().raw() == Symbols::SavedTryContextVar().raw())) {
+          (variable->name().raw() == Symbols::SavedTryContextVar().raw()) ||
+          (variable->name().raw() == Symbols::IteratorParameter().raw())) {
         // Don't capture those variables because the VM expects them to be on
         // the stack.
         continue;