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

utils/tests/pub/install/sdk/check_out_transitive_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('includes transitive dependencies', () {
     dir(sdkPath, [
       file('revision', '1234'),
       dir('pkg', [
         dir('foo', [
           libDir('foo', 'foo 0.0.1234'),
           libPubspec('foo', '0.0.0-not.used', [{'sdk': 'bar'}])
         ]),
@@ skipping 12 matching lines @@
         output: const RegExp(r"Dependencies installed!$"));
 
     packagesDir({
       'foo': '0.0.1234',
       'bar': '0.0.1234'
     }).scheduleValidate();
 
     run();
   });
 }