Fix language tests wrt. warnings.

tests/language/abstract_exact_selector_test.dart

 // Copyright (c) 2013, 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.
 
 // Regression test for dart2js that used to duplicate some `Object`
 // methods to handle `noSuchMethod`.
 
 import "package:expect/expect.dart";
 import "compiler_annotations.dart";
 
-abstract class Foo {
+abstract /// 01: static type warning
+class Foo {
   noSuchMethod(im) => 42;
 }
 
 @DontInline()
 returnFoo() {
   (() => 42)();
   return new Foo();
 }
 
 class Bar {
   operator==(other) => false;
 }
 
 var a = [false, true, new Object(), new Bar()];
 
 main() {
   if (a[0]) {
     // This `==` call will make the compiler create a selector with an
     // exact `TypeMask` of `Foo`. Since `Foo` is abstract, such a call
     // cannot happen, but we still used to generate a `==` method on
     // the `Object` class to handle `noSuchMethod`.
     print(returnFoo() == 42);
   } else {
     Expect.isFalse(a[2] == 42);
   }
 }