Make int.gcd accept zero operands.

runtime/lib/integers.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.
 
 // TODO(srdjan): fix limitations.
 // - shift amount must be a Smi.
 class _IntegerImplementation extends _Num {
   // The Dart class _Bigint extending _IntegerImplementation requires a
   // default constructor.
 
@@ skipping 373 matching lines @@
       throw new UnsupportedError("Not coprime");
     }
     return _binaryGcd(m, t, true);
   }
 
   // Returns gcd of abs(this) and abs(other), with this != 0 and other !=0.
   int gcd(int other) {
     if (other is! int) {
       throw new ArgumentError.value(other, "other", "not an integer");
     }
-    if (this == 0) {
-      throw new ArgumentError.value(this, "first operand", "must not be zero");
-    }
-    if (other == 0) {
-      throw new ArgumentError.value(this, "second operand", "must not be zero");
+    if ((this == 0) && (other == 0)) {
+      throw new ArgumentError.value(0, null,
+                                    "at least one operand must not be zero");
     }
     int x = this.abs();
     int y = other.abs();
+    if (x == 0) return y;
+    if (y == 0) return x;
     if ((x == 1) || (y == 1)) return 1;
     if (other is _Bigint) {
       return _toBigint().gcd(other);
     }
     return _binaryGcd(x, y, false);
   }
 }
 
 class _Smi extends _IntegerImplementation implements int {
   factory _Smi._uninstantiable() {
@@ skipping 207 matching lines @@
   // Shift by mint exceeds range that can be handled by the VM.
   int _shrFromInt(int other) {
     if (other < 0) {
       return -1;
     } else {
       return 0;
     }
   }
   int _shlFromInt(int other) native "Mint_shlFromInt";
 }