Count closures using the feedback vector cell map, specialize if count==1.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 243b10b222a0a662165d57a82a46b852d1ddf7f4..59467798eb0f7b78b3dea770a648d269bcd695c6 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -12118,7 +12118,8 @@ void JSFunction::EnsureLiterals(Handle<JSFunction> function) {
       // A top level script didn't get it's literals installed.
       Handle<FeedbackVector> feedback_vector =
           FeedbackVector::New(isolate, shared);
-      Handle<Cell> new_cell = isolate->factory()->NewCell(feedback_vector);
+      Handle<Cell> new_cell =
+          isolate->factory()->NewOneClosureCell(feedback_vector);
       function->set_feedback_vector_cell(*new_cell);
       break;
     }