Re-land beginning Dart 2.0 test migration.

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 //# 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);
-  }
-}