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

BUG=458915
TEST=Select 2000 photos by Ctrl+A and check that UI responds in less than 500ms.

Review URL: https://codereview.chromium.org/973483002

Cr-Commit-Position: refs/heads/master@{#318853}

ui/file_manager/file_manager/foreground/js/directory_contents.js

@@ -580,6 +580,11 @@ FileListContext.createPrefetchPropertyNames_ = function() {
   for (var i = 0; i < Command.METADATA_PREFETCH_PROPERTY_NAMES.length; i++) {
     set[Command.METADATA_PREFETCH_PROPERTY_NAMES[i]] = true;
   }
+  for (var i = 0;
+       i < FileSelection.METADATA_PREFETCH_PROPERTY_NAMES.length;
+       i++) {
+    set[FileSelection.METADATA_PREFETCH_PROPERTY_NAMES[i]] = true;
+  }
   return Object.keys(set);
 };
 

ui/file_manager/file_manager/foreground/js/file_selection.js

@@ -103,6 +103,17 @@ function FileSelection(fileManager, indexes) {
   }
 }
 
+/**
+ * Metadata property names used by FileSelection.
+ * These metadata is expected to be cached to accelerate completeInit() of
+ * FileSelection. crbug.com/458915.
+ * @const {!Array<string>}
+ */
+FileSelection.METADATA_PREFETCH_PROPERTY_NAMES = [
+  'availableOffline',
+  'contentMimeType',
+];
+
 /**
  * Computes data required to get file tasks and requests the tasks.
  * @return {!Promise}

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]);
     }
   }