Introduce NUMBER_IS_FINITE macro to avoid ToNumber() conversion.

src/string.js

 // Copyright 2006-2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 109 matching lines @@
 
 // ECMA-262 section 15.5.4.8
 function StringLastIndexOf(pat /* position */) {  // length == 1
   var sub = TO_STRING_INLINE(this);
   var subLength = sub.length;
   var pat = TO_STRING_INLINE(pat);
   var patLength = pat.length;
   var index = subLength - patLength;
   if (%_ArgumentsLength() > 1) {
     var position = ToNumber(%_Arguments(1));
-    if (!$isNaN(position)) {
+    if (!NUMBER_IS_NAN(position)) {
       position = TO_INTEGER(position);
       if (position < 0) {
         position = 0;
       }
       if (position + patLength < subLength) {
         index = position
       }
     }
   }
   if (index < 0) {
@@ skipping 770 matching lines @@
     "italics", StringItalics,
     "small", StringSmall,
     "strike", StringStrike,
     "sub", StringSub,
     "sup", StringSup
   ));
 }
 
 
 SetupString();