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

src/factory.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/factory.h"
 
 #include "src/allocation-site-scopes.h"
 #include "src/base/bits.h"
 #include "src/bootstrapper.h"
 #include "src/conversions.h"
@@ skipping 2211 matching lines @@
     int num = Handle<Smi>::cast(number)->value();
     str = IntToCString(num, buffer);
   } else {
     double num = Handle<HeapNumber>::cast(number)->value();
     str = DoubleToCString(num, buffer);
   }
 
   // We tenure the allocated string since it is referenced from the
   // number-string cache which lives in the old space.
   Handle<String> js_string = NewStringFromAsciiChecked(str, TENURED);
-  // Make sure the string cached in the number cache is also the internalized
-  // version of the same string.
-  js_string = InternalizeString(js_string);
   SetNumberStringCache(number, js_string);
   return js_string;
 }
 
 
 Handle<DebugInfo> Factory::NewDebugInfo(Handle<SharedFunctionInfo> shared) {
   // Allocate initial fixed array for active break points before allocating the
   // debug info object to avoid allocation while setting up the debug info
   // object.
   Handle<FixedArray> break_points(
@@ skipping 146 matching lines @@
 }
 
 
 Handle<Object> Factory::ToBoolean(bool value) {
   return value ? true_value() : false_value();
 }
 
 
 }  // namespace internal
 }  // namespace v8