Change restrictions on start/end on String.fromCharCodes.

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 88 matching lines @@
    *
    *     new String.fromCharCodes([68]); // 'D'
    *
    * If a char-code value is greater than 16-bits, it is decomposed into a
    * surrogate pair:
    *
    *     var clef = new String.fromCharCodes([0x1D11E]);
    *     clef.codeUnitAt(0); // 0xD834
    *     clef.codeUnitAt(1); // 0xDD1E
    *
-   * If [start] is provided, the first `start` elements of `charCodes` are
-   * skipped. If `charCodes` has fewer than `start` elements in all, the
-   * result is an empty string. The `start` value must be non-negative.
-   *
-   * If [end] is provided, any elements of `charCodes` after the `end`'th are
-   * ignored. If `charCodes` has fewer than `end` elements, the `end` parameter
-   * has no effect.
+   * If [start] and [end] is provided, only the values of [charCodes]
+   * at positions from `start` to, but not including, `end`, are used.
+   * The `start` and `end` values must satisfy
+   * `0 <= start <= end <= charCodes.length`.
    */
   external factory String.fromCharCodes(Iterable<int> charCodes,
                                         [int start = 0, int end]);
 
   /**
    * 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
@@ skipping 619 matching lines @@
         _position = position - 1;
         _currentCodePoint = _combineSurrogatePair(prevCodeUnit, codeUnit);
         return true;
       }
     }
     _position = position;
     _currentCodePoint = codeUnit;
     return true;
   }
 }