Avoid UI jankiness caused by triggering selection scan too frequently.

ui/file_manager/file_manager/foreground/js/import_controller.js

Index: ui/file_manager/file_manager/foreground/js/import_controller.js
diff --git a/ui/file_manager/file_manager/foreground/js/import_controller.js b/ui/file_manager/file_manager/foreground/js/import_controller.js
index 0d129a01b06d6768247b07dd7de2deb87e08ac75..8659572986716a7f1d0d382d9121425fb6f19738 100644
--- a/ui/file_manager/file_manager/foreground/js/import_controller.js
+++ b/ui/file_manager/file_manager/foreground/js/import_controller.js
@@ -1211,7 +1211,7 @@ importer.RuntimeControllerEnvironment.prototype.addDirectoryChangedListener =
 importer.RuntimeControllerEnvironment.prototype.addSelectionChangedListener =
     function(listener) {
   this.selectionHandler_.addEventListener(
-      FileSelectionHandler.EventType.CHANGE,
+      FileSelectionHandler.EventType.CHANGE_THROTTLED,
       listener);
 };