Divide volume_manager.js into files for each classes and extract interfaces from them.

ui/file_manager/file_manager/background/js/media_import_handler_unittest.html

Index: ui/file_manager/file_manager/background/js/media_import_handler_unittest.html
diff --git a/ui/file_manager/file_manager/background/js/media_import_handler_unittest.html b/ui/file_manager/file_manager/background/js/media_import_handler_unittest.html
index ceabb6f1239fcf52de19c908454c257569938fb0..742c2153bc45777994b4fee460575d62412613b6 100644
--- a/ui/file_manager/file_manager/background/js/media_import_handler_unittest.html
+++ b/ui/file_manager/file_manager/background/js/media_import_handler_unittest.html
@@ -25,6 +25,7 @@
   <script src="../../common/js/progress_center_common.js"></script>
   <script src="../../common/js/test_tracker.js"></script>
 
+  <script src="entry_location_impl.js"></script>
   <script src="test_import_history.js"></script>
   <script src="mock_progress_center.js"></script>
   <script src="mock_media_scanner.js"></script>
@@ -33,7 +34,11 @@
   <script src="media_import_handler.js"></script>
   <script src="duplicate_finder.js"></script>
   <script src="test_duplicate_finder.js"></script>
-  <script src="volume_manager.js"></script>
+  <script src="volume_info_impl.js"></script>
+  <script src="volume_info_list_impl.js"></script>
+  <script src="volume_manager_factory.js"></script>
+  <script src="volume_manager_impl.js"></script>
+  <script src="volume_manager_util.js"></script>
   <script src="file_operation_util.js"></script>
 
   <script src="media_import_handler_unittest.js"></script>