Revert "Remove Expect from core library."

tests/language/getter_no_setter2_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.
 // Verifies behavior with a static getter, but no field and no setter.
 
-import "package:expect/expect.dart";
-
 class Example {
   static int _var = 1;
   static int get nextVar => _var++;
   Example() {
     {
       bool flag_exception = false;
       try {
         nextVar++;
       } catch (excpt) {
         flag_exception = true;
@@ skipping 24 matching lines @@
   static int _var = 1;
   static int get nextVar => _var++;
   Example2() : super(nextVar) { }  // No 'this' in scope.
 }
 
 void main() {
   Example x = new Example();
   Example.test();
   Example2 x2 = new Example2();
 }