Revert "Remove Expect from core library."

tests/standalone/double_to_int_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.
 //
 // Tests optimization: transform double.toInt() to DoubleToSmi
 // unless we encounter a non-Smi result, in which case we deoptimize and
 // optimize it later to DoubleToInt.
 
-import "package:expect/expect.dart";
-
 
 main() {
   for (int i = 0; i < 600; i++) {
     Expect.equals(100, foo(100, 1.2));
   }
   // Deoptimize 'foo', d2smi -> d2int.
   Expect.equals(36507222016 * 2, foo(2, 36507222016.6));
   for (int i = 0; i < 600; i++) {
     Expect.equals(100, foo(100, 1.2));
   }
   Expect.equals(36507222016 * 2, foo(2, 36507222016.6));
 }
 
 
 foo(n, a) {
   int k = 0;
   for (int i = 0; i < n; i++) {
     k += goo(a);
   }
   return k;
 }
 
 
 goo(a) {
   return a.toInt();
 }