Get rid of use of dart:html in unittestlib.

client/testing/unittest/unittest_dom.dart

-// Copyright (c) 2011, 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.
-
-// Version of unittest library that directly uses the dom library versions of
-// 'window' and 'document', and avoids using the html library.
-
-// TODO: When it is possible to use both dom and html in the same program
-// (i.e. using namespaces to distinguish the two global window() getters),
-// remove one of the versions.
-
-#library("unittest");
-
-#import("dart:dom");
-
-#source("unittestsuite.dart");