Revert "Remove Expect from core library."

tests/language/number_constant_folding1_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";
-
 // On frogsh constant folded hex literals of large magnitude were truncated on
 // constant folding - Issue 636 is 'fixed', remaining concerns at Issue 638.
 
 
 highDigitTruncationTest() {
   Expect.equals(0x12345678A, 0x123456789 + 1);
 
   // in 32 bits this is 0xF0000000 which is negative.
   Expect.isTrue(0x1f0000000 > 0);
 
   Expect.equals(0xf0, 0xf * 16);
   Expect.equals(0xff0, 0xff * 16);
   Expect.equals(0xfff0, 0xfff * 16);
   Expect.equals(0xffff0, 0xffff * 16);
   Expect.equals(0xfffff0, 0xfffff * 16);
   Expect.equals(0xffffff0, 0xffffff * 16);
   Expect.equals(0xfffffff0, 0xfffffff * 16);
   Expect.equals(0xffffffff0, 0xffffffff * 16);
   Expect.equals(0xfffffffff0, 0xfffffffff * 16);
   Expect.equals(0xffffffffff0, 0xffffffffff * 16);
 }
 
 
 main() {
   highDigitTruncationTest();
 }