Revert "Remove Expect from core library."

tests/language/branches_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.
 // Dart test for branches. Make sure that shortcuts work, even if they have
 // to jump over several expressions.
 
-import "package:expect/expect.dart";
-
 class BranchesTest {
   static bool f() {
     Expect.equals("Never reached", 0);
     return true;
   }
 
   static void testMain() {
     int checkPointCounter = 1;
     int checkPoint1 = 0;
     int checkPoint2 = 0;
@@ skipping 130 matching lines @@
     Expect.equals(4, checkPoint3);
     Expect.equals(0, checkPoint4);
     Expect.equals(8, checkPoint5);
     Expect.equals(6, checkPoint6);
   }
 }
 
 main() {
   BranchesTest.testMain();
 }