Make int.gcd accept zero operands.

sdk/lib/_internal/compiler/js_lib/js_number.dart

Index: sdk/lib/_internal/compiler/js_lib/js_number.dart
diff --git a/sdk/lib/_internal/compiler/js_lib/js_number.dart b/sdk/lib/_internal/compiler/js_lib/js_number.dart
index 8d7501e1e99a68e79cd5eaaad4c313a8cbeac4fd..fb13d38e5f7f2e9970a49e7cccf9afe84f7dedc3 100644
--- a/sdk/lib/_internal/compiler/js_lib/js_number.dart
+++ b/sdk/lib/_internal/compiler/js_lib/js_number.dart
@@ -504,14 +504,14 @@ class JSInt extends JSNumber implements int, double {
     if (m is! int) {
       throw new ArgumentError.value(m, "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(this, 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;
     return _binaryGcd(x, y, false);
   }