Revert "Remove Expect from core library."

tests/compiler/dart2js/return_type_inferer_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.
 
-import "package:expect/expect.dart";
 import '../../../sdk/lib/_internal/compiler/implementation/ssa/ssa.dart';
 
 import 'compiler_helper.dart';
 
 const String TEST_ONE = r"""
   f(p) { if (p == null) return p; else return p; }
   main() { f("s"); }
 """;
 
 const String TEST_TWO = r"""
@@ skipping 69 matching lines @@
   runTest(TEST_SIX, HType.NUMBER);
   runTest(TEST_SEVEN);
   runTest(TEST_EIGHT, HType.INTEGER);
   runTest(TEST_NINE);
   runTest(TEST_TEN);
 }
 
 void main() {
   test();
 }