Fix probably harmless thinko in StringCharAt (causes

slow-case code to be run).
Review URL: http://codereview.chromium.org/43005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1470 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/string.js

@@ -62,7 +62,7 @@ function StringValueOf() {
 
 // ECMA-262, section 15.5.4.4
 function StringCharAt(pos) {
-  var char_code = %_FastCharCodeAt(subject, index);
+  var char_code = %_FastCharCodeAt(this, index);
   if (!%_IsSmi(char_code)) {
     var subject = ToString(this);
     var index = TO_INTEGER(pos);