Files app: Stop auto-generating JS module for externs folder

* background_window.js
* command_handler_deps.js
* directory_change_event.js
* drive_dialog_controller.js
* entries_changed_event.js
* entry_location.js
* exif_entry.js
* files_app_entry_interfaces.js
* metadata_worker_window.js
* progress_center_panel.js
* volume_manager.js
* volume_info.js
* volume_info_list.js

Bug: 1214953
Change-Id: I06c310608c49cef951e2b20ca0c9d5cdb63f95aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2973255
Commit-Queue: Luciano Pacheco <lucmult@chromium.org>
Auto-Submit: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Jeremie Boulic <jboulic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#894639}

diff --git a/ui/file_manager/file_manager/BUILD.gn b/ui/file_manager/file_manager/BUILD.gn
index 3d8d88c..ebd51b596 100644
--- a/ui/file_manager/file_manager/BUILD.gn
+++ b/ui/file_manager/file_manager/BUILD.gn

@@ -32,6 +32,11 @@
     # For some unittests:
     "foreground/js/metadata/image_orientation.js",
     "externs/background/background_base.js",
+    "externs/entry_location.js",
+    "externs/files_app_entry_interfaces.js",
+    "externs/volume_info.js",
+    "externs/volume_info_list.js",
+    "externs/volume_manager.js",
 
     # CSS:
     "foreground/css/combobutton.css",