Show UI when a folder is empty.

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

 /* Copyright (c) 2014 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. */
 
 /* Special attribute used in HTML to hide elements. */
 body[type='folder'] [invisibleif~='folder'],
 body[type='upload-folder'] [invisibleif~='upload-folder'],
 body[type='saveas-file'] [invisibleif~='saveas-file'],
 body[type='open-file'] [invisibleif~='open-file'],
 body[type='open-multi-file'] [invisibleif~='open-multi-file'],
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   padding: 10px;
   position: absolute;
   right: 0;
   top: 36px;  /* Leave room for the file list header. */
 }
 
 .dialog-container:not([drive-welcome='page']) #no-search-results[show] {
   display: block;
 }
 
+#empty-folder {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+  justify-content: center;
+  left: 0;
+  position: absolute;
+  top: 0;
+  width: 100%;
+}
+
+#empty-folder > .image {
+  background-image: -webkit-image-set(
+      url(../images/files/ui/empty_folder.png) 1x,
+      url(../images/files/ui/2x/empty_folder.png) 2x);
+  height: 145px;
+  margin: 50px auto 32px auto;
+  width: 120px;
+}
+
+#empty-folder > .label {
+  color: rgb(180, 180, 180);
+  font-size: 16px;
+  font-weight: bold;
+  text-align: center;
+}
+
 #volume-space-info-contents {
   align-items: center;
   display: flex;
 }
 
 #volume-space-info-contents > div {
   -webkit-margin-start: 15px;
   display: flex;
   flex: auto;
 }
@@ skipping 394 matching lines @@
   padding: 20px 15px;
 }
 
 .text-measure {
   pointer-events: none;
   position: absolute;
   top: 0;
   visibility: hidden;
   z-index: -1;
 }