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

tests/html/instance_of_test.dart

-#library('InstanceOfTest');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
+library InstanceOfTest;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
 
 main() {
   CanvasElement canvas;
 
   canvas = new Element.tag('canvas');
   canvas.attributes['width'] = 100;
   canvas.attributes['height'] = 100;
   document.body.nodes.add(canvas);
 
   var isCanvasRenderingContext = predicate((x) => x is CanvasRenderingContext,
@@ skipping 46 matching lines @@
     expect(bytes, isNot(isCanvasElement));
     expect(bytes, isNot(isImageData));
     expect(bytes, isUint8ClampedArray);
 
     // FIXME: Ensure this is an SpanElement when we next update
     // WebKit IDL.
     var span = new Element.tag('span');
     expect(span, isElement);
   });
 }