Enable strict flags for all service tests

runtime/observatory/test/echo_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 --checked
 
 import 'dart:async';
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 
 var tests = [
 
 (Isolate isolate) =>
   isolate.vm.invokeRpc('_echo', { 'text': 'hello'}).then((result) {
@@ skipping 18 matching lines @@
       completer.complete();
     }
   });
   isolate.invokeRpc('_triggerEchoEvent', { 'text': 'hello' });
   return completer.future;
 },
 
 ];
 
 main(args) => runIsolateTests(args, tests);