Revert "Remove Expect from core library."

tests/language/intrinsified_methods_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 the instanceof operation.
 
 library intrinsified_methods_test;
-import "package:expect/expect.dart";
 import 'dart:math';
 
 testIsNegative() {
   Expect.isFalse((12.0).isNegative);
   Expect.isTrue((-12.0).isNegative);
   Expect.isFalse((double.NAN).isNegative);
   Expect.isFalse((0.0).isNegative);
   Expect.isTrue((-0.0).isNegative);
   Expect.isFalse((double.INFINITY).isNegative);
   Expect.isTrue((double.NEGATIVE_INFINITY).isNegative);
@@ skipping 18 matching lines @@
     testIsNegative();
     testIsNaN();
     testTrigonometric();
   }
   return x;
 }
 
 void main() {
   var m = foo(4000);
 }