Fix static warnings in Observatory tests.

runtime/observatory/test/async_generator_breakpoint_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=--verbose-debug
 
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 import 'dart:async';
@@ skipping 48 matching lines @@
   var bp4 = await isolate.addBreakpoint(script, 21);
   expect(bp4, isNotNull);
   expect(bp4 is Breakpoint, isTrue);
   var bp5 = await isolate.addBreakpoint(script, 39);
   expect(bp5, isNotNull);
   expect(bp5 is Breakpoint, isTrue);
 
   var hits = [];
 
   isolate.eval(isolate.rootLib, 'testerReady = true;')
-      .then((ServiceObject result) {
+      .then((Instance result) {
         expect(result.valueAsString, equals('true'));
       });
 
   await for (ServiceEvent event in isolate.vm.events.stream) {
     if (event.eventType == ServiceEvent.kPauseBreakpoint) {
       var bp = event.breakpoint;
       print('Hit $bp');
       hits.add(bp);
       isolate.resume();
 
       if (hits.length == 5) break;
     }
   }
 
   expect(hits, equals([bp1, bp5, bp4, bp2, bp3]));
 }
 
 var tests = [testAsync];
 
 main(args) => runIsolateTests(args, tests, testeeConcurrent: testeeDo);