Port metrics to RPC

runtime/observatory/test/native_metrics_test.dart

+import 'package:observatory/service_io.dart';
+import 'package:unittest/unittest.dart';
+import 'test_helper.dart';
+
+import 'dart:profiler';
+
+void script() {
+  var counter = new Counter('a.b.c', 'description');
+  Metrics.register(counter);
+  counter.value = 1234.5;
+}
+
+var tests = [
+
+(Isolate isolate) =>
+    isolate.refreshNativeMetrics().then((Map metrics) {
+      expect(metrics.length, greaterThan(1));
+      expect(metrics.length, greaterThan(1));
+      var foundOldHeapCapacity = metrics.values.any((m) =>
+          m.name == 'heap.old.capacity');
+      expect(foundOldHeapCapacity, equals(true));
+  }),
+
+(Isolate isolate) =>
+  isolate.invokeRpc('getIsolateMetric',
+                    { 'metricId': 'metrics/native/heap.old.used' })
+      .then((ServiceMetric counter) {
+    expect(counter.type, equals('Counter'));
+    expect(counter.name, equals('heap.old.used'));
+  }),
+
+(Isolate isolate) =>
+    isolate.invokeRpc('getIsolateMetric',
+                      { 'metricId': 'metrics/native/doesnotexist' })
+          .then((DartError err) {
+    expect(err is DartError, isTrue);
+  }),
+
+];
+
+main(args) => runIsolateTests(args, tests, testeeBefore: script);