Make sure to flatten names before lookup. Lookup using cons strings is really slow.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 4a683405bd40980d9d93f23d62727aa0800da62e..f5ce1d6c4251ff0582b4ec7fa7d1cb10aea7ff21 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -8592,6 +8592,11 @@ class Name: public HeapObject {
   // If the name is private, it can only name own properties.
   inline bool IsPrivate();
 
+  // If the name is a non-flat string, this method returns a flat version of the
+  // string. Otherwise it'll just return the input.
+  static inline Handle<Name> Flatten(Handle<Name> name,
+                                     PretenureFlag pretenure = NOT_TENURED);
+
   DECLARE_CAST(Name)
 
   DECLARE_PRINTER(Name)