Let operator* in Duration accept doubles.

tests/corelib/duration_big_num_test.dart

+// Copyright (c) 2013, 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.
+
+import "package:expect/expect.dart";
+import 'dart:math';
+
+main() {
+  Duration d, d1;
+
+  d1 = new Duration(microseconds: pow(2, 53));
+  d = d1 * 2;
+  Expect.equals(pow(2, 54), d.inMicroseconds);
+  d = d1 * 1.5;
+  Expect.equals(pow(2, 53).toDouble() * 1.5, d.inMicroseconds);
+  Expect.isTrue(d.inMicroseconds is int);
+
+  // Test that we lose precision when multiplying with a double.
+  d = new Duration(microseconds: pow(2, 53) + 1) * 1.0;
+  Expect.equals(0, d.inMicroseconds % 2);
+}
+