Optimize String.fromCharCode.

sdk/lib/core/string.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.core;
 
 /**
  * A sequence of characters.
  *
  * A string can be either single or multiline. Single line strings are
@@ skipping 98 matching lines @@
   external factory String.fromCharCodes(Iterable<int> charCodes);
 
   /**
    * Allocates a new String for the specified [charCode].
    *
    * If the [charCode] can be represented by a single UTF-16 code unit, the new
    * string contains a single code unit. Otherwise, the [length] is 2 and
    * the code units form a surrogate pair. See documentation for
    * [fromCharCodes].
    *
-   * Creating a String with half of a surrogate pair is legal but generally
-   * discouraged.
+   * Creating a String with half of a surrogate pair is allowed.
    */
-  factory String.fromCharCode(int charCode) {
-    List<int> charCodes = new List<int>.filled(1, charCode);
-    return new String.fromCharCodes(charCodes);
-  }
+  external factory String.fromCharCode(int charCode);
 
   /**
    * Returns the string value of the environment declaration [name].
    *
    * Environment declarations are provided by the surrounding system compiling
    * or running the Dart program. Declarations map a string key to a string
    * value.
    *
    * If [name] is not declared in the environment, the result is instead
    * [defaultValue].
@@ skipping 595 matching lines @@
         _position = position - 1;
         _currentCodePoint = _combineSurrogatePair(prevCodeUnit, codeUnit);
         return true;
       }
     }
     _position = position;
     _currentCodePoint = codeUnit;
     return true;
   }
 }