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

Index: sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
diff --git a/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart b/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
index 279ee270849d8dd3f34dc94de87ee8f05a6af0d6..52d2f67198d0cfcede2005bf2f66f1deb950975d 100644
--- a/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
+++ b/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
@@ -535,6 +535,16 @@ class Primitives {
 
   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);