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

tests/html/location_test.dart

-#library('LocationTest');
-#import('../../pkg/unittest/unittest.dart');
-#import('../../pkg/unittest/html_config.dart');
-#import('dart:html');
+library LocationTest;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
 
 main() {
   useHtmlConfiguration();
 
   var isLocation = predicate((x) => x is Location, 'is a Location');
 
   test('location hash', () {
       final location = window.location;
       expect(location, isLocation);
 
       // The only navigation we dare try is hash.
       location.hash = 'hello';
       var h = location.hash;
       expect(h, '#hello');
     });
 }