Let stopwatch use window.performance.now when available. Fix for: http://code.google.com/p/dart/iss…

sdk/lib/_internal/compiler/implementation/lib/core_patch.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.
 
 // Patch file for dart:core classes.
 
 // Patch for 'print' function.
 patch void print(var object) {
   if (object is String) {
     Primitives.printString(object);
@@ skipping 130 matching lines @@
   patch int get second => Primitives.getSeconds(this);
 
   patch int get millisecond => Primitives.getMilliseconds(this);
 
   patch int get weekday => Primitives.getWeekday(this);
 }
 
 
 // Patch for Stopwatch implementation.
 patch class _StopwatchImpl {
-  patch static int _frequency() => 1000;
-  patch static int _now() => Primitives.dateNow();
+  patch static int _frequency() => 1000000;
+  patch static int _now() => Primitives.numMicroseconds();
 }
 
 
 // Patch for List implementation.
 patch class List<E> {
   patch factory List([int length]) => Primitives.newList(length);
 }
 
 
 patch class String {
@@ skipping 41 matching lines @@
 }
 
 patch class RegExp {
   patch factory RegExp(String pattern,
                        {bool multiLine: false,
                         bool ignoreCase: false})
     => new JSSyntaxRegExp(pattern,
                           multiLine: multiLine,
                           ignoreCase: ignoreCase);
 }