Fix all Observatory warnings/errors.

runtime/observatory/test/isolate_lifecycle_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 --checked
 
 import 'dart:async';
 import 'dart:isolate' as I;
-import 'dart:math';
 
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 
 import 'test_helper.dart';
 
 final spawnCount = 4;
 final resumeCount = spawnCount ~/ 2;
 final isolates = [];
 
 void spawnEntry(int i) {
 }
 
 Future before() async {
   // Spawn spawnCount long lived isolates.
   for (var i = 0; i < spawnCount; i++) {
     var isolate = await I.Isolate.spawn(spawnEntry, i);
     isolates.add(isolate);
   }
   print('spawned all isolates');
 }
 
-Future during() {
+Future during() async {
 }
 
 var tests = [
   (VM vm) async {
     expect(vm.isolates.length, spawnCount + 1);
   },
   (VM vm) async {
     // Load each isolate.
     for (var isolate in vm.isolates) {
       await isolate.load();
@@ skipping 51 matching lines @@
     }
     expect(pausedCount, spawnCount - resumeCount);
     expect(runningCount, 1);
   },
 ];
 
 main(args) async => runVMTests(args, tests,
                                testeeBefore: before,
                                testeeConcurrent: during,
                                pause_on_exit: true);