Enabled Mosaic view on each volume.

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

Index: chrome/browser/resources/file_manager/css/gallery.css
diff --git a/chrome/browser/resources/file_manager/css/gallery.css b/chrome/browser/resources/file_manager/css/gallery.css
index bea91d1cef1cdf2c081ca995e768c848fcb8372e..8d820b278410e3da6f3114358205a378a6c19267 100644
--- a/chrome/browser/resources/file_manager/css/gallery.css
+++ b/chrome/browser/resources/file_manager/css/gallery.css
@@ -1228,9 +1228,20 @@ body {
   top: 0;
 }
 
-.mosaic-tile img {
-  -webkit-user-drag: none;
-  position: absolute;
+.mosaic-tile .img-wrapper[generic-thumbnail],
+.mosaic-tile .img-wrapper:not([generic-thumbnail]) canvas {
+  -webkit-animation: fadeIn ease-in 1;
+  -webkit-animation-duration: 500ms;
+  -webkit-animation-fill-mode: forwards;
+}
+
+@-webkit-keyframes fadeIn {
+  from {
+    opacity: 0;
+  }
+  to {
+    opacity: 1;
+  }
 }
 
 /* In order to do mode animated transitions smoothly we keep both mosaic and