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

tests/html/async_window_test.dart

Index: tests/html/async_window_test.dart
===================================================================
--- tests/html/async_window_test.dart	(revision 14313)
+++ tests/html/async_window_test.dart	(working copy)
@@ -1,7 +1,7 @@
-#library('AsyncWindowTest');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
+library AsyncWindowTest;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
 
 main() {
   useHtmlConfiguration();