Revert "Remove Expect from core library."

tests/standalone/constant_left_shift_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.
 //
 // Dart test program for testing left shifts of a constant.
 
-import "package:expect/expect.dart";
-
 shiftLeft0(c) => 0 << c;
 shiftLeft1(c) => 1 << c;
 shiftLeft8448(c) => 8448 << c;
 
 shiftLeftNeg1(c) => -1 << c;
 shiftLeftNeg8448(c) => -8448 << c;
 
 main() {
   // Optimize shifts.
   for (int i = 0; i < 6000; i++) {
@@ skipping 52 matching lines @@
   // Deoptimize on 32-bit.
   Expect.equals(-1107296256, shiftLeftNeg8448(17));
   Expect.equals(-2214592512, shiftLeftNeg8448(18));
   Expect.equals(-1188950301625810944, shiftLeftNeg8448(47));
   Expect.equals(-2377900603251621888, shiftLeftNeg8448(48));
   // Deoptimize on 64 bits.
   Expect.equals(-4755801206503243776, shiftLeftNeg8448(49));
   Expect.equals(-9511602413006487552, shiftLeftNeg8448(50));
 }