[shared_preferences] driver test using package:test on device (#1285)

* Add SharedPreference example driver test

packages/shared_preferences/example/pubspec.yaml

diff --git a/packages/shared_preferences/example/pubspec.yaml b/packages/shared_preferences/example/pubspec.yaml
index 68f61bd..8661855 100644
--- a/packages/shared_preferences/example/pubspec.yaml
+++ b/packages/shared_preferences/example/pubspec.yaml
@@ -7,5 +7,10 @@
   shared_preferences:
     path: ../
 
+dev_dependencies:
+  flutter_driver:
+    sdk: flutter
+  test: any
+
 flutter:
   uses-material-design: true