Files.app: Mitigate performance issue on select-all by prefetching content mime type.

ui/file_manager/file_manager/foreground/js/file_transfer_controller.js

Index: ui/file_manager/file_manager/foreground/js/file_transfer_controller.js
diff --git a/ui/file_manager/file_manager/foreground/js/file_transfer_controller.js b/ui/file_manager/file_manager/foreground/js/file_transfer_controller.js
index 5ef1622cb1c61bb221ed04b94f73b89926399da7..26acbe0f16b1a38541735665f7dd06f15f2179c9 100644
--- a/ui/file_manager/file_manager/foreground/js/file_transfer_controller.js
+++ b/ui/file_manager/file_manager/foreground/js/file_transfer_controller.js
@@ -1093,9 +1093,11 @@ FileTransferController.prototype.onFileSelectionChangedThrottled_ = function() {
   // asynchronous operations.
   if (!containsDirectory) {
     for (var i = 0; i < fileEntries.length; i++) {
-      fileEntries[i].file(function(data, file) {
-        data.file = file;
-      }.bind(null, asyncData[fileEntries[i].toURL()]));
+      (function(fileEntry) {
+        fileEntry.file(function(file) {
+          asyncData[fileEntry.toURL()].file = file;
+        });
+      })(fileEntries[i]);
     }
   }