Fix all Observatory warnings/errors.

runtime/observatory/test/call_site_data_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
 
 library call_site_data_test;
 
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
-import 'dart:async';
 
 class A { foo() => 'A'; }
 class B { foo() => 'B'; }
 class C { foo() => 'C'; }
 class D { foo() => 'D'; }
 class E { foo() => 'E'; }
 class F { foo() => 'F'; }
 class G { foo() => 'G'; }
 class H { foo() => 'H'; }
 
@@ skipping 158 matching lines @@
 var tests = [
     testMonomorphic,
     testPolymorphic,
     testMegamorphic,
     testStaticCall,
     testConstructorCall,
     testTopLevelCall,
     testSuperCall ];
 
 main(args) => runIsolateTests(args, tests, testeeBefore: script);