Use shared implementation of Stopwatch.

dart/frog/leg/lib/mock.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.
 
 // Mocks of things that Leg cannot read directly.
 
 // TODO(ahe): Remove this file.
 
 class AssertionError {}
 class TypeError extends AssertionError {}
 class FallThroughError {}
 
 // TODO(ahe): VM specfic exception?
 class InternalError {}
 
 // TODO(ahe): VM specfic exception?
 class StaticResolutionException implements Exception {}
 
 class List<E> implements Iterable<E> {
   factory List([int length]) => Primitives.newList(length);
   factory List.from(Iterable<E> other) {
     throw 'List.from is not implemented';
   }
 }
 
-class Stopwatch {
-  double startMs;
-  double elapsedMs;
-
-  Stopwatch() {
-    elapsedMs = 0.0;
-  }
-
-  void start() {
-    if (startMs == null) {
-      startMs = Primitives.dateNow();
-    }
-  }
-
-  void stop() {
-    if (startMs == null) return;
-    elapsedMs += Primitives.dateNow() - startMs;
-    startMs = null;
-  }
-
-  void reset() {
-    elapsedMs = 0.0;
-    if (startMs == null) return;
-    startMs = Primitives.dateNow();
-  }
-
-  int elapsed() {
-    return elapsedInMs();
-  }
-
-  int elapsedInUs() {
-    return elapsedInMs() * 1000;
-  }
-
-  int elapsedInMs() {
-    if (startMs == null) {
-      return Primitives.mathFloor(elapsedMs);
-    } else {
-      return Primitives.mathFloor(elapsedMs + (Primitives.dateNow() - startMs));
-    }
-  }
-
-  int frequency() {
-    return 1000;
-  }
-}
-
 void assert(condition) {}