Make int.gcd accept zero operands.

sdk/lib/_internal/compiler/js_lib/js_number.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 _interceptors;
 
 /**
  * The super interceptor class for [JSInt] and [JSDouble]. The compiler
  * recognizes this class as an interceptor, and changes references to
  * [:this:] to actually use the receiver of the method, which is
@@ skipping 486 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 (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);
   }
 
   // Assumes i is <= 32-bit and unsigned.
   static int _bitCount(int i) {
     // See "Hacker's Delight", section 5-1, "Counting 1-Bits".
 
     // The basic strategy is to use "divide and conquer" to
     // add pairs (then quads, etc.) of bits together to obtain
@@ skipping 38 matching lines @@
 }
 
 class JSDouble extends JSNumber implements double {
   const JSDouble();
   Type get runtimeType => double;
 }
 
 class JSPositiveInt extends JSInt {}
 class JSUInt32 extends JSPositiveInt {}
 class JSUInt31 extends JSUInt32 {}