Revert "Remove Expect from core library."

tests/language/call_operator_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";
-
 
 // simple test with no types in signature
 class A1 {
   call() => 42;
 }
 
 // same test, include return type
 class A2 {
   int call() => 35;
 }
@@ skipping 55 matching lines @@
   Expect.equals("foo", e("foo"));
   Expect.equals("foo:foo", e("foo", count:2));
   Expect.equals("foo:foo:foo", e("foo", count:3));
   Expect.equals("foo", e.call("foo"));
   Expect.equals("foo:foo", e.call("foo", count:2));
   Expect.equals("foo:foo:foo", e.call("foo", count:3));
 
   Expect.isTrue(a1 is Function);
   Expect.isTrue(e is Function);
 }