Revert "Remove Expect from core library."

tests/language/invocation_mirror_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";
-
 // InvocationMirror and noSuchMethod testing.
 
 /** Class with noSuchMethod that returns the mirror */
 class N {
   // Storage for the last argument to noSuchMethod.
   // Needed for setters, which don't evaluate to the return value.
   var last;
   noSuchMethod(InvocationMirror m) => last = m;
 
   flif(int x) { Expect.fail("never get here"); }
@@ skipping 220 matching lines @@
   test(() => o.hashCode = 42);
   test(() => o.hashCode());  // Thrown by int.noSuchMethod.
   test(() => (n.flif)());  // Extracted method has no noSuchMethod.
 }
 
 main() {
   testInvocationMirrors();
   testNoSuchMethodErrors();
   new M().testSuperCalls();
 }