Revert "Remove Expect from core library."

tests/language/bailout_test.dart

 // Copyright (c) 2012, 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.
 
-import "package:expect/expect.dart";
-
 // Test that a call to a bailout method in dart2js resolves to the
 // right method.
 
 var reachedAfoo = new C();
 
 class A {
   foo() {
     // Using '++' makes sure there is a type guard.
     reachedAfoo++;
   }
@@ skipping 22 matching lines @@
 main() {
   // Using a loop makes sure the 'foo' methods will have an optimized
   // version.
   while (reachedAfoo.value != 0) {
     new A().foo();
     new B().foo();
   }
   new B().bar();
   Expect.equals(1, reachedAfoo.value);
 }