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

pkg/intl/test/intl_message_basic_example_test.dart

Index: pkg/intl/test/intl_message_basic_example_test.dart
===================================================================
--- pkg/intl/test/intl_message_basic_example_test.dart	(revision 14440)
+++ pkg/intl/test/intl_message_basic_example_test.dart	(working copy)
@@ -11,7 +11,7 @@
 import '../lib/intl.dart';
 import '../lib/message_lookup_local.dart';
 import '../example/basic/basic_example.dart';
-import '../../unittest/unittest.dart';
+import '../../../pkg/unittest/lib/unittest.dart';
 
 List list;
 
@@ -30,4 +30,4 @@
   expect(list[2], "วิ่ง 0:00:00 on วันพฤหัสบดี 1 มกราคม 1970.");
   expect(list[3], "วิ่ง now on today.");
   });
-}
+}