Revert "Remove Expect from core library."

tests/language/generic_creation_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 A<X, Y, Z> {
   shift() => new A<Z, X, Y>();
   swap() => new A<Z, Y, X>();
   first() => new A<X, X, X>();
   last() => new A<Z, Z, Z>();
   wrap() => new A<A<X, X, X>, A<Y, Y, Y>, A<Z, Z, Z>>();
 }
 
 class B extends A<U, V, W> {}
 
@@ skipping 14 matching lines @@
   sameType(new A<U, U, U>(), a.first());
   sameType(new A<W, W, W>(), a.last());
   sameType(new A<A<U, U, U>, A<V, V, V>, A<W, W, W>>(), a.wrap());
   B b = new B();
   sameType(new A<A<U, U, U>, A<V, V, V>, A<W, W, W>>(), b.wrap());
   C c = new C<V>();
   sameType(new A<A<U, U, U>, A<V, V, V>, A<W, W, W>>(), c.wrap());
   D d = new D<U, V, W>();
   sameType(new A<A<V, V, V>, A<W, W, W>, A<U, U, U>>(), d.wrap());
 }