Change removable storage inotify to scan /storage

Since we are exposing /storage instead of /var/run/arc/media/removable
inside ARC++ container, we should also request scan through /storage so
that MediaScanner is not confused.

BUG=b:69078137
TEST=Manually verified. Google Photos doesn't show duplicate device
anymore (before, it shows one for /storage and one for
/var/run/arc/media/removable).

Change-Id: I93e9f029068110983d6033348acb9f2e85fd5f89
Reviewed-on: https://chromium-review.googlesource.com/c/1329820Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Reviewed-by: Ryo Hashimoto <hashimoto@chromium.org>
Commit-Queue: Risan <risan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609989}

chrome/browser/chromeos/arc/file_system_watcher/arc_file_system_watcher_service.cc

@@ -50,10 +50,9 @@ constexpr base::FilePath::CharType kCrosRemovableMediaDir[] =
     FILE_PATH_LITERAL("/media/removable");
 
 // The removable media path inside ARC container. This will be the path that
-// is used in MediaScanner.scanFile request. The /var is mandatory here because
-// it is the ARC container side path name.
+// is used in MediaScanner.scanFile request.
 constexpr base::FilePath::CharType kAndroidRemovableMediaDir[] =
-    FILE_PATH_LITERAL("/var/run/arc/media/removable");
+    FILE_PATH_LITERAL("/storage");
 
 // How long to wait for new inotify events before building the updated timestamp
 // map.