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

tests/html/document_test.dart

-#library('DocumentTest');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
+library DocumentTest;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
 
 main() {
   useHtmlConfiguration();
 
   var isElement = predicate((x) => x is Element, 'is an Element');
   var isDivElement = predicate((x) => x is DivElement, 'is a DivElement');
   var isAnchorElement =
       predicate((x) => x is AnchorElement, 'is an AnchorElement');
   var isUnknownElement =
       predicate((x) => x is UnknownElement, 'is UnknownElement');
 
   test('CreateElement', () {
     // FIXME: nifty way crashes, do it boring way.
     expect(new Element.tag('span'), isElement);
     expect(new Element.tag('div'), isDivElement);
     expect(new Element.tag('a'), isAnchorElement);
     expect(new Element.tag('bad_name'), isUnknownElement);
   });
 }