Revert "Remove Expect from core library."

tests/language/class_literal_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 class literal expressions.
 
 class Class {
   static fisk() => 42;
 }
 
 foo(x) {}
 
 main() {
   if (false) {
@@ skipping 40 matching lines @@
   // Verify that a class literal isn't a string literal.
   Expect.notEquals(Class, "Class");
    
   // Verify toString() works for class literals.
   Expect.equals((Class).toString(), "Class");
   var y = Class;
   Expect.equals(y.toString(), "Class");
   
   Expect.throws(() { Class.toString(); }, (e) => e is NoSuchMethodError);
 }