Revert "Remove Expect from core library."

tests/language/named_parameters_with_dollars_test.dart

 // Copyright (c) 2011, 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 to stress Frog's named parameter scheme.
 
 main() {
   testDollar();
   testPsycho();
 }
 
 class TestClass {
   method({a, b, a$b, a$$b}) => [a, b, a$b, a$$b];
 
@@ skipping 60 matching lines @@
   Expect.equals('[1, 2, -, -]', format(t.psycho($:1, $$:2)));
   Expect.equals('[-, -, -, 4]', format(t.psycho($$$$: 4)));
 
   var obj = makeTestClass(0);
 
   Expect.equals('[1, 2, -, -]', format(obj.psycho($:1, $$:2)));
   Expect.equals('[-, -, -, 4]', format(obj.psycho($$$$: 4)));
   Expect.equals('[1, 2, 3, -]', format(obj.psycho($:1, $$:2, $$$:3)));
   Expect.equals('[1, 2, 3, -]', format(obj.psycho($$$:3, $$:2, $:1)));
 }