Add VMMetric and some sample metrics

runtime/bin/vmservice/observatory/test/vm_metrics_test.dart

Index: runtime/bin/vmservice/observatory/test/vm_metrics_test.dart
diff --git a/runtime/bin/vmservice/observatory/test/metrics_test.dart b/runtime/bin/vmservice/observatory/test/vm_metrics_test.dart
similarity index 55%
copy from runtime/bin/vmservice/observatory/test/metrics_test.dart
copy to runtime/bin/vmservice/observatory/test/vm_metrics_test.dart
index 170835f42f4e05e3f99d17486219880fd5c69c55..349f212d8a19ab188cbed60a3608ff84d9587ab8 100644
--- a/runtime/bin/vmservice/observatory/test/metrics_test.dart
+++ b/runtime/bin/vmservice/observatory/test/vm_metrics_test.dart
@@ -13,24 +13,24 @@ void script() {
 var tests = [
 
 (Isolate isolate) =>
-  isolate.get('metrics').then((ServiceMap metrics) {
+  isolate.get('metrics/vm').then((ServiceMap metrics) {
     expect(metrics['type'], equals('MetricList'));
     var members = metrics['members'];
     expect(members, isList);
-    expect(members.length, equals(1));
-    var counter = members[0];
-    expect(counter['name'], equals('a.b.c'));
-    expect(counter['value'], equals(1234.5));
+    expect(members.length, greaterThan(1));
+    var foundOldHeapCapacity = members.any((m) =>
+        m['name'] == 'heap.old.capacity');
+    expect(foundOldHeapCapacity, equals(true));
 }),
 
 (Isolate isolate) =>
-  isolate.get('metrics/a.b.c').then((ServiceMap counter) {
-    expect(counter['name'], equals('a.b.c'));
-    expect(counter['value'], equals(1234.5));
+  isolate.get('metrics/vm/heap.old.used').then((ServiceMap counter) {
+    expect(counter['type'], equals('Counter'));
+    expect(counter['name'], equals('heap.old.used'));
 }),
 
 (Isolate isolate) =>
-  isolate.get('metrics/a.b.d').then((DartError err) {
+  isolate.get('metrics/vm/doesnotexist').then((DartError err) {
     expect(err is DartError, isTrue);
 }),