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

tests/html/element_classes_test.dart

 // Copyright (c) 2011, 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('ElementTest');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
+library ElementTest;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
 
 main() {
   useHtmlConfiguration();
 
   Element makeElement() => new Element.tag('div');
 
   Element makeElementWithChildren() =>
     new Element.html("<div><br/><img/><input/></div>");
 
   Element makeElementWithClasses() =>
@@ skipping 140 matching lines @@
     expect(classes.intersection(['foo', 'qux', 'baz']),
         unorderedEquals(['foo', 'baz']));
   });
 
   test('clear', () {
     final classes = makeClassSet();
     classes.clear();
     expect(classes, equals([]));
   });
 }