Remove Expect from core library.

tests/language/cascade_2_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";
+
 // Test cascades, issues 7494 (vm), 7689 (dart2js).
 
 main() {
   var a = new Element(null);
   Expect.equals(1, a.path0.length);
   Expect.equals(a, a.path0[0]);
 
   // Issue 7693: e0 ? e1 : e2..f() parses as (e0 ? e1 : e2)..f().
   Expect.equals(2, a.path1.length);
   Expect.equals(a, a.path1[0]);
@@ skipping 29 matching lines @@
   }
 
   List<Element> get path1 {
     return (parent == null) ? <Element>[this] : parent.path1..add(this);
   }
 
   List<Element> get path2 {
     return (parent == null) ? <Element>[this] : (parent.path2..add(this));
   }
 }