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 a4088c18d7c3c6cadee60c61ef9660f53773496a..2a92752425a10ce6ebe4d80a2a18466ce488b584 100644
--- a/ui/file_manager/file_manager/foreground/css/file_manager.css
+++ b/ui/file_manager/file_manager/foreground/css/file_manager.css
@@ -392,6 +392,12 @@ body.check-select #delete-button > .icon {
       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;
 }