Revert "Remove Expect from core library."

tests/language/statement_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";
-
 // Tests all statement types. Not an exhaustive test of all statement semantics.
 class StatementTest {
 
   StatementTest() {}
 
   static testMain() {
     var test = new StatementTest();
     test.testIfStatement();
     test.testForLoop();
     test.testWhileLoops();
@@ skipping 185 matching lines @@
     if (true) {
       return;
     }
     Expect.equals(true, false);
   }
 }
 
 main() {
   StatementTest.testMain();
 }