Let operator* in Duration accept doubles.

sdk/lib/core/duration.dart

 // Copyright (c) 2011, 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 dart.core;
 
 /**
  * A [Duration] represents a time span. A duration can be negative.
  */
 class Duration implements Comparable<Duration> {
@@ skipping 64 matching lines @@
    * Returns the difference of this [Duration] and [other] as a new
    * [Duration].
    */
   Duration operator -(Duration other) {
     return new Duration(microseconds: _duration - other._duration);
   }
 
   /**
    * Multiplies this [Duration] by the given [factor] and returns the result
    * as a new [Duration].
+   *
+   * Note that when [factor] is a double, and the duration is greater than
+   * 53 bits, precision is lost because of double-precision arithmetic.
    */
-  Duration operator *(int factor) {
-    return new Duration(microseconds: _duration * factor);
+  Duration operator *(num factor) {
+    return new Duration(microseconds: (_duration * factor).round());
   }
 
   /**
    * Divides this [Duration] by the given [quotient] and returns the truncated
    * result as a new [Duration].
    *
    * Throws an [IntegerDivisionByZeroException] if [quotient] is `0`.
    */
   Duration operator ~/(int quotient) {
     // By doing the check here instead of relying on "~/" below we get the
@@ skipping 76 matching lines @@
           new Duration(microseconds: -inMicroseconds);
       return "-$duration";
     }
     String twoDigitMinutes = twoDigits(inMinutes.remainder(MINUTES_PER_HOUR));
     String twoDigitSeconds = twoDigits(inSeconds.remainder(SECONDS_PER_MINUTE));
     String sixDigitUs =
         sixDigits(inMicroseconds.remainder(MICROSECONDS_PER_SECOND));
     return "$inHours:$twoDigitMinutes:$twoDigitSeconds.$sixDigitUs";
   }
 }