Restructure pkg/unittest and pkg/webdriver to follow the pub conventions.

utils/tests/pub/install/hosted/do_not_update_on_removed_constraints_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.
 
 library pub_tests;
 
 import 'dart:io';
 
 import '../../test_pub.dart';
-import '../../../../../pkg/unittest/unittest.dart';
+import '../../../../../pkg/unittest/lib/unittest.dart';
 
 main() {
   test("doesn't update dependencies whose constraints have been removed", () {
     servePackages([
       package("foo", "1.0.0", [dependency("shared-dep")]),
       package("bar", "1.0.0", [dependency("shared-dep", "<2.0.0")]),
       package("shared-dep", "1.0.0"),
       package("shared-dep", "2.0.0")
     ]);
 
@@ skipping 15 matching lines @@
 
     packagesDir({
       "foo": "1.0.0",
       "bar": null,
       "shared-dep": "1.0.0"
     }).scheduleValidate();
 
     run();
   });
 }