Use WeakCells in the optimized code map rather than traversing in pause.

src/factory.cc

Index: src/factory.cc
diff --git a/src/factory.cc b/src/factory.cc
index 79f2ef1cae3d0372267975caca0039b66ff6c8b5..42056853c059c6dde29a7d436e00600b6a7f6f60 100644
--- a/src/factory.cc
+++ b/src/factory.cc
@@ -728,6 +728,8 @@ Handle<Context> Factory::NewNativeContext() {
   Handle<Context> context = Handle<Context>::cast(array);
   context->set_js_array_maps(*undefined_value());
   context->set_errors_thrown(Smi::FromInt(0));
+  Handle<WeakCell> weak_cell = NewWeakCell(context);
+  context->set_self_weak_cell(*weak_cell);
   DCHECK(context->IsNativeContext());
   return context;
 }