Make int.gcd accept zero operands.

sdk/lib/core/int.dart

Index: sdk/lib/core/int.dart
diff --git a/sdk/lib/core/int.dart b/sdk/lib/core/int.dart
index 4bac632032baa1fed7516cdd5511107f2c9e7202..c9759db5978e541166a45af05a972ec64db949de 100644
--- a/sdk/lib/core/int.dart
+++ b/sdk/lib/core/int.dart
@@ -124,7 +124,7 @@ abstract class int extends num {
    * 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);