Revert "Remove Expect from core library."

tests/language/parameter_types_specialization_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.
 // Test that we invalidate parameter type optimization in the presence
 // of optional parameters.
 
-import "package:expect/expect.dart";
-
 class A {
   void foo(bool firstInvocation, [a = 42, b = 'foo']) {
     if (firstInvocation) {
       Expect.isTrue(a is String);
       Expect.isTrue(b is int);
     } else {
       Expect.isTrue(a is int);
       Expect.isTrue(b is String);
     }
   }
 }
 
 test() {
   // This call to [A.foo] will be in the queue after [A.foo] has been
   // compiled with the optimistic type assumptions.
   new A().foo(false);
 }
 
 main() {
   test();
   // This call to [A.foo] will be the first in the queue, and dart2js
   // will optimize the method with these parameter types.
   new A().foo(true, 'bar', 42);
 }