Revert "Remove Expect from core library."

tests/language/first_class_types_literals_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 C<T, U, V> {}
 
 class D {}
 
 typedef int Foo(bool b);
 
 sameType(a, b) {
   Expect.equals(a.runtimeType, b.runtimeType);
 }
 
@@ skipping 17 matching lines @@
   // runtimeType on type is idempotent.
   Expect.equals((D).runtimeType, (D).runtimeType.runtimeType);
 
   // Test that operator calls on class literals go to Type.
   Expect.throws(() => C = 1, (e) => e is NoSuchMethodError);
   Expect.throws(() => C++, (e) => e is NoSuchMethodError);
   Expect.throws(() => C + 1, (e) => e is NoSuchMethodError);
   Expect.throws(() => C[2], (e) => e is NoSuchMethodError);
   Expect.throws(() => C[2] = 'hest', (e) => e is NoSuchMethodError);
 }