Fix foreground file_transfer_controller BUILD rule

 - FileTransferController uses ProgressCenter in its contructor
   - add externs_list deps to externs backend ProgressCenter

No change in test behavior.

Bug: 914197
Change-Id: I12d91732edd9fec52c44af54d9c88a6e9f98719a
Reviewed-on: https://chromium-review.googlesource.com/c/1373050Reviewed-by: Sam McNally <sammc@chromium.org>
Reviewed-by: Stuart Langley <slangley@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615815}

ui/file_manager/file_manager/foreground/js/BUILD.gn

@@ -414,6 +414,7 @@ js_library("file_transfer_controller") {
     "ui:multi_profile_share_dialog",
     "ui:progress_center_panel",
   ]
+  externs_list = [ "../../../externs/background/progress_center.js" ]
 }
 
 js_library("file_watcher") {