Small improvement to String.fromCodePoint.

src/harmony-string.js

 // 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.
 
 'use strict';
 
 // This file relies on the fact that the following declaration has been made
 // in runtime.js:
 // var $String = global.String;
 // var $Array = global.Array;
@@ skipping 142 matching lines @@
     if (!%_IsSmi(code)) {
       code = ToNumber(code);
     }
     if (code < 0 || code > 0x10FFFF || code !== TO_INTEGER(code)) {
       throw MakeRangeError("invalid_code_point", [code]);
     }
     if (code <= 0xFFFF) {
       result += %_StringCharFromCode(code);
     } else {
       code -= 0x10000;
-      result += StringFromCharCode(
-        code >>> 10 & 0x3FF | 0xD800,
-        0xDC00 | code & 0x3FF
-      );
+      result += %_StringCharFromCode((code >>> 10) & 0x3FF | 0xD800);
+      result += %_StringCharFromCode(code & 0x3FF | 0xDC00);
     }
   }
   return result;
 }
 
 
 // -------------------------------------------------------------------
 
 function ExtendStringPrototype() {
   %CheckIsBootstrapping();
 
   // Set up the non-enumerable functions on the String object.
   InstallFunctions($String, DONT_ENUM, $Array(
     "fromCodePoint", StringFromCodePoint
   ));
 
   // Set up the non-enumerable functions on the String prototype object.
   InstallFunctions($String.prototype, DONT_ENUM, $Array(
     "codePointAt", StringCodePointAt,
     "contains", StringContains,
     "endsWith", StringEndsWith,
     "repeat", StringRepeat,
     "startsWith", StringStartsWith
   ));
 }
 
 ExtendStringPrototype();