Add a refresh button for providers which do not support watchers.

ui/file_manager/file_manager/foreground/css/file_manager.css

Index: ui/file_manager/file_manager/foreground/css/file_manager.css
diff --git a/ui/file_manager/file_manager/foreground/css/file_manager.css b/ui/file_manager/file_manager/foreground/css/file_manager.css
index 8c17045a42ad5cd3f3543e2e1d3e486965ec26cc..6f980aaf74b48ab86a5a9e67e80175b1f9b146ea 100644
--- a/ui/file_manager/file_manager/foreground/css/file_manager.css
+++ b/ui/file_manager/file_manager/foreground/css/file_manager.css
@@ -411,6 +411,12 @@ body.check-select #delete-button {
       url(../images/files/ui/2x/view_list_white.png) 2x);
 }
 
+#refresh-button > .icon {
+  background-image: -webkit-image-set(
+      url(../images/files/ui/refresh_white.png) 1x,
+      url(../images/files/ui/2x/refresh_white.png) 2x);
+}
+
 body.check-select #view-button {
   display: none;
 }