Don't internalize names that are array indexes since they aren't used for lookup (the index is)

src/lookup.cc

 // Copyright 2014 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.
 
 #include "src/lookup.h"
 
 #include "src/bootstrapper.h"
 #include "src/deoptimizer.h"
 #include "src/elements.h"
 #include "src/field-type.h"
@@ skipping 20 matching lines @@
   if (!*success) {
     DCHECK(isolate->has_pending_exception());
     // Return an unusable dummy.
     return LookupIterator(receiver, isolate->factory()->empty_string());
   }
 
   if (name->AsArrayIndex(&index)) {
     LookupIterator it(isolate, receiver, index, configuration);
     // Here we try to avoid having to rebuild the string later
     // by storing it on the indexed LookupIterator.
-    it.name_ = isolate->factory()->InternalizeName(name);
+    it.name_ = name;
     return it;
   }
 
   return LookupIterator(receiver, name, configuration);
 }
 
 
 void LookupIterator::Next() {
   DCHECK_NE(JSPROXY, state_);
   DCHECK_NE(TRANSITION, state_);
@@ skipping 622 matching lines @@
     // Fall through.
     default:
       return NOT_FOUND;
   }
   UNREACHABLE();
   return state_;
 }
 
 }  // namespace internal
 }  // namespace v8