Revert "Remove Expect from core library."

tests/language/scope_variable_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";
-
 class ScopeVariableTest {
 
   static void testSimpleScope() {
     {
       var a = "Test";
       int b = 1;
     }
     {
       var c;
       int d;
@@ skipping 15 matching lines @@
 
   static void testMain() {
     testSimpleScope();
     testShadowingScope();
   }
 }
 
 main() {
   ScopeVariableTest.testMain();
 }