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

tests/html/canvasrenderingcontext2d_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();
   var canvas = new CanvasElement();
   canvas.width = 100;
   canvas.height = 100;
 
   var context = canvas.context2d;
 
   Uint8ClampedArray readPixel() {
@@ skipping 92 matching lines @@
     context.fillStyle = 'green';
     context.fillRect(0, 0, canvas.width, canvas.height);
 
     context.putImageData(expectedData, 0, 0);
 
     var resultingData = context.getImageData(0, 0, 10, 10);
     // Make sure that we read back what we wrote.
     expect(resultingData.data, expectedData.data);
   });
 }