Immediately open MTP and other eligible removable devices with media directory on mount.

ui/file_manager/file_manager/background/js/device_handler_unittest.html

Index: ui/file_manager/file_manager/background/js/device_handler_unittest.html
diff --git a/ui/file_manager/file_manager/background/js/device_handler_unittest.html b/ui/file_manager/file_manager/background/js/device_handler_unittest.html
index 8b2500e5d507238a73faf164702ca3204dc39340..229c1d99d6f1f48de895b00315467bbba19f2822 100644
--- a/ui/file_manager/file_manager/background/js/device_handler_unittest.html
+++ b/ui/file_manager/file_manager/background/js/device_handler_unittest.html
@@ -9,13 +9,18 @@
 
 <script src="../../../../../ui/webui/resources/js/cr.js"></script>
 <script src="../../../../../ui/webui/resources/js/cr/event_target.js"></script>
+<script src="../../../../../ui/webui/resources/js/cr/ui/array_data_model.js"></script>
 <script src="../../../../../ui/webui/resources/js/load_time_data.js"></script>
 
 <!-- Need to load async_util.js before device_handler.js -->
 <script src="../../common/js/async_util.js"></script>
+<script src="../../common/js/unittest_util.js"></script>
+<script src="../../common/js/mock_entry.js"></script>
 <script src="../../common/js/volume_manager_common.js"></script>
 <script src="../../common/js/importer_common.js"></script>
 <script src="../../common/js/util.js"></script>
+<script src="mock_volume_manager.js"></script>
+<script src="volume_manager.js"></script>
 <script src="device_handler.js"></script>
 
 <script src="device_handler_unittest.js"></script>