Revert "Remove Expect from core library."

tests/compiler/dart2js_extra/no_such_method_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";
-
 class NoSuchMethodInfo {
   Object receiver;
   String name;
   List args;
   NoSuchMethodInfo(Object r, String m, List a)
     : receiver = r, name = m, args = a;
 }
 
 class A {
   noSuchMethod(InvocationMirror invocation) {
@@ skipping 28 matching lines @@
   Expect.isTrue(info.args.length == 0);
   Expect.isTrue(identical(info.receiver, a));
 
   a.bar = 2;
   info = topLevelInfo;
   Expect.equals('bar', info.name);
   Expect.isTrue(info.args.length == 1);
   Expect.isTrue(info.args[0] == 2);
   Expect.isTrue(identical(info.receiver, a));
 }