Do not JSON encode the 'result' of a service rpc.

runtime/observatory/tests/service/malformed_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.
 // 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';
 
 var tests = [
+  (Isolate isolate) async {
+    await isolate.invokeRpc('_respondWithMalformedObject', {}).then((result) {
+      expect(false, isTrue, reason:'Unreachable');
+    }).catchError((ServiceException exception) {
+      expect(exception.kind, equals('ResponseFormatException'));
+      expect(exception.message,
+             startsWith('Top level service responses must be service maps'));
+    });
+  },
 
-(Isolate isolate) =>
-  isolate.invokeRpc('_respondWithMalformedJson', { }).then((result) {
-    // Should not execute.
-    expect(true, false);
-  }).catchError((ServiceException exception) {
-    expect(exception.kind, equals('JSONDecodeException'));
-  }),
-
-(Isolate isolate) =>
-  isolate.invokeRpc('_respondWithMalformedObject', { }).then((result) {
-    // Should not execute.
-    expect(true, false);
-  }).catchError((ServiceException exception) {
-    expect(exception.kind, equals('ResponseFormatException'));
-  }),
+  // Do this test last... it kills the vm connection.
+  (Isolate isolate) async {
+    await isolate.invokeRpc('_respondWithMalformedJson', {}).then((result) {
+      expect(false, isTrue, reason:'Unreachable');
+    }).catchError((ServiceException exception) {
+      expect(exception.kind, equals('ConnectionClosed'));
+      expect(exception.message, startsWith('Error decoding JSON message'));
+    });
+  },
 ];
 
 main(args) => runIsolateTests(args, tests);