Gallery: Add items to GalleryDataModel before loading their metadata.

ui/file_manager/gallery/css/gallery.css

Index: ui/file_manager/gallery/css/gallery.css
diff --git a/ui/file_manager/gallery/css/gallery.css b/ui/file_manager/gallery/css/gallery.css
index 8a3eaf7f20bb728c4d3de9136d848d3354c1f1ee..ae798d15b684c7dc79497e53afad04ab6d2a2c9c 100644
--- a/ui/file_manager/gallery/css/gallery.css
+++ b/ui/file_manager/gallery/css/gallery.css
@@ -441,6 +441,7 @@ input[type='checkbox']:checked {
   height: 100%;
   overflow: hidden;
   transition: opacity 180ms linear, visibility 0ms linear;
+  white-space: nowrap;
   z-index: 0;
 }
 
@@ -455,7 +456,7 @@ input[type='checkbox']:checked {
   cursor: pointer;
   display: inline-block;
   height: 47px;
-  margin: 2px;
+  margin: 2px 2px 2px 0;
   overflow: hidden;
   transition: all 180ms linear;
   width: 47px;