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

utils/tests/pub/install/hosted/remove_removed_dependency_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("removes a dependency that's been removed from the pubspec", () {
     servePackages([
       package("foo", "1.0.0"),
       package("bar", "1.0.0")
     ]);
 
     appDir([dependency("foo"), dependency("bar")]).scheduleCreate();
 
@@ skipping 11 matching lines @@
         output: const RegExp(r"Dependencies installed!$"));
 
     packagesDir({
       "foo": "1.0.0",
       "bar": null
     }).scheduleValidate();
 
     run();
   });
 }