Revert "Remove Expect from core library."

tests/language/execute_finally9_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.
 // This test ensures that the finally block executes correctly when
 // there are throw, break and return statements in the finally block.
 
-import "package:expect/expect.dart";
-
 class Hello {
  static var sum;
 
  static foo() {
    sum = 0;
    try {
      sum += 1;
      return 'hi';
    } catch (e) {
      sum += 1;
@@ skipping 40 matching lines @@
      // Ignore.
    }
    Expect.equals(2, sum);
  }
 
 }
 
 main() {
   Hello.main();
 }