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

src/objects.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/allocation.h"
@@ skipping 8574 matching lines @@
   // Equality operations.
   inline bool Equals(Name* other);
   inline static bool Equals(Handle<Name> one, Handle<Name> two);
 
   // Conversion.
   inline bool AsArrayIndex(uint32_t* index);
 
   // 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)
 #if TRACE_MAPS
   void NameShortPrint();
   int NameShortPrint(Vector<char> str);
 #endif
 
   // Layout description.
   static const int kHashFieldSlot = HeapObject::kHeaderSize;
@@ skipping 2262 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_