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

tests/html/contentelement_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('contentelement_test');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
+library contentelement_test;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
 
 main() {
   useHtmlConfiguration();
 
   var isContentElement =
       predicate((x) => x is ContentElement, 'is a ContentElement');
 
   test('constructor', () {
       var e = new ContentElement();
       expect(e, isContentElement);
     });
 }