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

sdk/lib/_internal/compiler/implementation/lib/js_helper.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.
 
 library _js_helper;
 
 import 'dart:collection';
 
 part 'constant_map.dart';
 part 'native_helper.dart';
@@ skipping 517 matching lines @@
     if ((length is !int) || (length < 0)) {
       throw new ArgumentError(length);
     }
     var result = JS('=List', r'new Array(#)', length);
     JS('void', r'#.fixed$length = #', result, true);
     return result;
   }
 
   static num dateNow() => JS('num', r'Date.now()');
 
+  static num numMicroseconds() {
+    var performance = JS('var', 'window.performance');

[ngeoffray, 2012/11/21 08:32:53]

Shouldn't you check that window is defined too?

+    if (performance != null && 
+        JS('bool', 'typeof #.webkitNow == "function"', performance)) {
+      return JS('num', '#.webkitNow()', performance);
+    } else {
+      return 1000 * dateNow();
+    }
+  }
+
   static String stringFromCharCodes(charCodes) {
     for (var i in charCodes) {
       if (i is !int) throw new ArgumentError(i);
     }
     return JS('String', r'String.fromCharCode.apply(#, #)', null, charCodes);
   }
 
   static String getTimeZoneName(receiver) {
     // When calling toString on a Date it will emit the timezone in parenthesis.
     // Example: "Wed May 16 2012 21:13:00 GMT+0200 (CEST)".
@@ skipping 988 matching lines @@
     return typeName == other.typeName;
   }
 }
 
 String getRuntimeTypeString(var object) {
   var typeInfo = JS('var', r'#.builtin$typeInfo', object);
   return JS('String', r'#.runtimeType', typeInfo);
 }
 
 createRuntimeType(String name) => new TypeImpl(name);