Rework error handling in the service protocol and in Observatory.

runtime/observatory/tests/service/native_metrics_test.dart

 // Copyright (c) 2015, 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.
 // VMOptions=--compile-all --error_on_bad_type --error_on_bad_override
 
 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) async {
+    Map metrics = await isolate.refreshNativeMetrics();
+    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) {
+  (Isolate isolate) async {
+    var params = { 'metricId': 'metrics/native/heap.old.used' };
+    ServiceMetric counter =
+      await isolate.invokeRpc('getIsolateMetric', params);
     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);
-  }),
+  (Isolate isolate) async {
+    bool caughtException;
+    try {
+      await isolate.invokeRpc('getIsolateMetric',
+                              { 'metricId': 'metrics/native/doesnotexist' });
+      expect(false, isTrue, reason:'Unreachable');
+    } on ServerRpcException catch (e) {
+      caughtException = true;
+      expect(e.code, equals(ServerRpcException.kInvalidParams));
+      expect(e.message,
+             "getIsolateMetric: invalid 'metricId' "
+             "parameter: metrics/native/doesnotexist");
+    }
+    expect(caughtException, isTrue);
+  },
 
 ];
 
 main(args) => runIsolateTests(args, tests, testeeBefore: script);