Make int.gcd accept zero operands.

sdk/lib/core/int.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;
 
 /**
  * An arbitrarily large integer.
  *
  * **Note:** When compiling to JavaScript, integers are
@@ skipping 106 matching lines @@
    *
    * The [modulus] must be positive.
    * Throws an [UnsupportedError] if no modular inverse exists.
    */
   int modInverse(int modulus);
 
   /**
    * Returns the greatest common divisor of the absolute value of
    * this integer and the absolute value of [other].
    *
-   * Both this and [other] must be non-zero.
+   * Either this or [other] must be non-zero.
    */
   int gcd(int other);
 
   /** Returns true if and only if this integer is even. */
   bool get isEven;
 
   /** Returns true if and only if this integer is odd. */
   bool get isOdd;
 
   /**
@@ skipping 163 matching lines @@
    *     var value = int.parse(text, onError: (source) => null);
    *     if (value == null) ... handle the problem
    *
    * The [onError] function is only invoked if [source] is a [String]. It is
    * not invoked if the [source] is, for example, `null`.
    */
   external static int parse(String source,
                             { int radix,
                               int onError(String source) });
 }