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

tests/html/events_test.dart

-#library('EventsTest');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
+library EventsTest;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
 
 main() {
   useHtmlConfiguration();
   test('TimeStamp', () {
     Event event = new Event('test');
 
     int timeStamp = event.timeStamp;
     expect(timeStamp, greaterThan(0));
   });
   // The next test is not asynchronous because [on['test'].dispatch(event)] fires the event
@@ skipping 36 matching lines @@
     invocationCounter = 0;
     element.on['test'].dispatch(event);
     expect(invocationCounter, 1);
   });
   test('InitMouseEvent', () {
     DivElement div = new Element.tag('div');
     MouseEvent event = document.$dom_createEvent('MouseEvent');
     event.$dom_initMouseEvent('zebra', true, true, window, 0, 1, 2, 3, 4, false, false, false, false, 0, div);
   });
 }