Make int.gcd accept zero operands.

runtime/lib/integers.dart

Index: runtime/lib/integers.dart
diff --git a/runtime/lib/integers.dart b/runtime/lib/integers.dart
index 90c3cddce053d69f6ece17f83b23fefd2af74f31..63f868bfdd23568c7431f4facfea3f895f1124d5 100644
--- a/runtime/lib/integers.dart
+++ b/runtime/lib/integers.dart
@@ -390,19 +390,15 @@ class _IntegerImplementation extends _Num {
     return _binaryGcd(m, t, true);
   }
 
-  // Returns gcd of abs(this) and abs(other), with this != 0 and other !=0.
+  // Returns gcd of abs(this) and abs(other).
   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, "this", "must not be zero");
-    }
-    if (other == 0) {
-      throw new ArgumentError.value(this, "other", "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);