Revert "Remove Expect from core library."

tests/compiler/dart2js_extra/static_var_no_initializer_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";
-
 int one;
 int x;
 
 void testOne() {
   Expect.equals(1, one);
 }
 
 void testX(var expected) {
   Expect.equals(expected, x);
 }
 
 void increaseX() {
   x = x + 1;
 }
 
 void main() {
   one = 1;
   x = 5;
   Expect.equals(1, one);
   testOne();
   Expect.equals(5, x);
   testX(5);
   x = x + 1;
   Expect.equals(6, x);
   testX(6);
   increaseX();
   Expect.equals(7, x);
   testX(7);
 }