Implemented one-char cache lookup in generated code.

src/runtime.js

 // Copyright 2006-2008 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 460 matching lines @@
 }
 
 
 // Specialized version of String.charAt. It assumes string as
 // the receiver type and that the index is a number.
 function STRING_CHAR_AT(pos) {
   var char_code = %_FastCharCodeAt(this, pos);
   if (!%_IsSmi(char_code)) {
     return %StringCharAt(this, pos);
   }
-  return %CharFromCode(char_code);
+  return %_CharFromCode(char_code);
 }
 
 
 /* -------------------------------------
    - - -   C o n v e r s i o n s   - - -
    -------------------------------------
 */
 
 // ECMA-262, section 9.1, page 30. Use null/undefined for no hint,
 // (1) for number hint, and (2) for string hint.
@@ skipping 147 matching lines @@
   throw %MakeTypeError('cannot_convert_to_primitive', []);
 }
 
 
 // NOTE: Setting the prototype for Array must take place as early as
 // possible due to code generation for array literals.  When
 // generating code for a array literal a boilerplate array is created
 // that is cloned when running the code.  It is essiential that the
 // boilerplate gets the right prototype.
 %FunctionSetPrototype($Array, new $Array(0));