Revert "Remove Expect from core library."

tests/compiler/dart2js_extra/constant_javascript_semantics_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.
 
-import "package:expect/expect.dart";
-
 // Make sure we use JavaScript semantics when compiling compile-time constants.
 
 const x = 12345678901234567891;
 const y = 12345678901234567890;
 const z = x - y;
 
 const a = 1.0;
 const b = a << 3;  // This would not be valid with Dart semantics.
 
 const c = -0.0;
@@ skipping 10 matching lines @@
   Expect.equals(8, b);
   Expect.equals(8, 1.0 << 3);  // This would not be valid with Dart semantics.
   Expect.isTrue(1 == 1.0);
   Expect.equals(0, d);
   Expect.equals(0, -0.0 << 1);  // This would not be valid with Dart semantics.
   // Make sure the 1 is not shifted into the 32 bit range.
   Expect.equals(0, 0x100000000 >> 3);
   // The dynamic int-check also allows -0.0.
   Expect.isTrue((-0.0) is int);
 }