[filebrowser] Enable sharing in gallery. For now, show all image-related extensions as 'Sharing'.

chrome/browser/resources/file_manager/js/image_editor/gallery.css

 /*
  * Copyright (c) 2011 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 body {
   margin: 0;
 }
 
@@ skipping 274 matching lines @@
   padding: 0 10px;
 
   display: -webkit-box;
   -webkit-box-orient: horizontal;
   -webkit-box-align: center;
 }
 
 .gallery .edit-modal > .range {
   margin: 4px 10px 4px 0;
 }
+
+.gallery .share-menu {
+  position: absolute;
+  right: 10px;
+  bottom: 80px;
+  background-color: rgba(240,240,240,1);;
+  opacity: 1.0;
+  -webkit-transition: opacity 0.5s ease-in-out;
+  padding: 10px;
+  display: -webkit-box;
+  -webkit-box-orient: vertical;
+  -webkit-box-align: stretch;
+  -webkit-box-pack: start;
+}
+
+.gallery .share-menu[hidden] {
+  opacity: 0.0;
+  pointer-events: none;
+}
+
+.gallery .share-menu > div {
+  cursor: pointer;
+  background-color: rgba(0,0,0,0);
+  padding: 5px;
+  display: -webkit-box;
+  -webkit-box-align: center;
+  -webkit-box-pack: start;
+}
+
+.gallery .share-menu > div:hover {
+  background-color: rgba(200,200,200,1);
+}
+
+.gallery .share-menu > div > img {
+  margin-right: 5px;
+}