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

tests/html/url_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('url_test');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
+library url_test;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
 
 main() {
   useHtmlConfiguration();
 
   Blob createImageBlob() {
     var canvas = new CanvasElement();
     canvas.width = 100;
     canvas.height = 100;
 
     var context = canvas.context2d;
@@ skipping 46 matching lines @@
       img.on.load.add((_) {
         guardAsync(() {
           expect(true, isFalse, reason: 'URL should not have loaded.');
         });
       });
       img.src = url;
     });
 
   });
 }