Revert "Remove Expect from core library."

tests/language/no_such_method2_test.dart

 // Copyright (c) 2013, 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";
-
 // Regression test for https://code.google.com/p/dart/issues/detail?id=7697.
 // dart2js used to optimize [noSuchMethod] based on the user-provided
 // argument, and forget that the runtime might call it with its own
 // [InvocationMirror] implementation.
 
 class Hey {
   foo() => noSuchMethod(new FakeInvocationMirror());
   noSuchMethod(x) => x;
 }
 
 class You extends Hey {
   // We used to think this method is always called with a
   // FakeInvocationMirror instance, but it's also called with the
   // internal mirror implementation.
   noSuchMethod(x) => x.isGetter;
 }
 
 class FakeInvocationMirror implements InvocationMirror {
   final bool isGetter = false;
 }
 
 main() {
   var x = new Hey();
   Expect.isTrue(x.foo() is FakeInvocationMirror);
   var y = [new You()];
   Expect.isTrue(y[0].bar);
 }