Remove Expect from core library.

tests/compiler/dart2js_extra/closure_capture_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";
+
 closure0() {
   var x = 499;
   // TODO(floitsch): remove name from functions.
   var f = fun() { return x; };
   Expect.equals(499, f());
 }
 
 class A {
   closure1() {
     var x = 499;
@@ skipping 67 matching lines @@
   new A().closure1();
   closure2();
   closure3();
   closure4();
   closure5();
   new A2().closure6();
   closure7();
   closure8();
   closure9();
 }