Convert the small packages in pkg to use "package:".

pkg/webdriver/test/webdrivertest.dart

 library webdriver_test;
-import '../webdriver.dart';
-import '../../../pkg/unittest/lib/unittest.dart';
+import 'package:webdriver/webdriver.dart';
+import 'package:unittest/unittest.dart';
 
 WebDriver web_driver;
 
 /**
  * These tests are not expected to be run as part of normal automated testing,
  * as they are slow, many of them do not yet work due to WebDriver limitations,
  * and they have external dependencies. Nontheless it is useful to keep them
  * here for manual testing.
  */
 main() {
@@ skipping 398 matching lines @@
         //print(logs);
         return session.close();
       }).then((_) {
         session = null;
         completionCallback();
       });
     });
   });
 }