Use shared implementation of Stopwatch.

dart/frog/leg/lib/clock.dart

Index: dart/frog/leg/lib/clock.dart
diff --git a/dart/frog/leg/lib/clock.dart b/dart/frog/leg/lib/clock.dart
new file mode 100644
index 0000000000000000000000000000000000000000..c9a1edddd15be7a3e7bbad1f1694246929a778f8
--- /dev/null
+++ b/dart/frog/leg/lib/clock.dart
@@ -0,0 +1,20 @@
+// 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.
+
+/**
+ * The class [Clock] provides access to a monotonically incrementing clock
+ * device.
+ */
+class Clock {
+
+  /**
+   * Returns the current clock tick.
+   */
+  static int now() => Primitives.dateNow();
+
+  /**
+   * Returns the frequency of clock ticks in Hz.
+   */
+  static int frequency() => 1000;
+}