Add VMMetric and some sample metrics

tests/lib/profiler/metrics_test.dart

 // Copyright (c) 2014, 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.
 //
 
 import 'dart:profiler';
 import 'package:expect/expect.dart';
 
 testGauge1() {
   var gauge = new Gauge('test', 'alpha bravo', 0.0, 100.0);
@@ skipping 81 matching lines @@
   Metrics.deregister(counter);
   Metrics.register(counter);
   var counter3 = new Counter('a.b.c.d', '');
   Metrics.register(counter3);
 }
 
 testBadName() {
   Expect.throws(() {
     var counter = new Counter('a.b/c', 'description');
   });
+  Expect.throws(() {
+    var counter = new Counter('vm', 'description');
+  });
 }
 
 main() {
   testGauge1();
   testGauge2();
   testCounter();
   testCustomCounter();
   testMetricNameCollision();
   testBadName();
 }