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

utils/tests/pub/install/hosted/resolve_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('resolves version constraints from a pub server', () {
     servePackages([
       package("foo", "1.2.3", [dependency("baz", ">=2.0.0")]),
       package("bar", "2.3.4", [dependency("baz", "<3.0.0")]),
       package("baz", "2.0.3"),
       package("baz", "2.0.4"),
       package("baz", "3.0.1")
     ]);
@@ skipping 11 matching lines @@
 
     packagesDir({
       "foo": "1.2.3",
       "bar": "2.3.4",
       "baz": "2.0.4"
     }).scheduleValidate();
 
     run();
   });
 }