Reuse File objects in FileTransferController.

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

 // Copyright (c) 2012 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.
 
 /**
  * Global (placed in the window object) variable name to hold internal
  * file dragging information. Needed to show visual feedback while dragging
  * since DataTransfer object is in protected state. Reachable from other
  * file manager instances.
  */
@@ skipping 1243 matching lines @@
   doc.addEventListener(command, handler);
   doc.execCommand(command);
   doc.removeEventListener(command, handler);
 };
 
 /**
  * @private
  */
 FileTransferController.prototype.onFileSelectionChanged_ = function() {
   this.preloadedThumbnailImagePromise_ = null;
-  this.selectedAsyncData_ = {};
 };
 
 /**
  * @private
  */
 FileTransferController.prototype.onFileSelectionChangedThrottled_ = function() {
+  // Remove file objects that are no longer in the selection.
+  var asyncData = {};
   var entries = this.selectionHandler_.selection.entries;
-  var asyncData = this.selectedAsyncData_;
+  for (var i = 0; i < entries.length; i++) {
+    var entryUrl = entries[i].toURL();
+    if (entryUrl in this.selectedAsyncData_) {
+      asyncData[entryUrl] = this.selectedAsyncData_[entryUrl];
+    }
+  }
+  this.selectedAsyncData_ = asyncData;
+
   var fileEntries = [];
   for (var i = 0; i < entries.length; i++) {
     if (entries[i].isFile)
       fileEntries.push(entries[i]);
-    asyncData[entries[i].toURL()] = {externalFileUrl: '', file: null};
+    if (!(entries[i].toURL() in asyncData)) {
+      asyncData[entries[i].toURL()] = {externalFileUrl: '', file: null};
+    }
   }
   var containsDirectory = this.selectionHandler_.selection.directoryCount > 0;
 
   // File object must be prepeared in advance for clipboard operations
   // (copy, paste and drag). DataTransfer object closes for write after
   // returning control from that handlers so they may not have
   // asynchronous operations.
   if (!containsDirectory) {
     for (var i = 0; i < fileEntries.length; i++) {
       (function(fileEntry) {
-        fileEntry.file(function(file) {
-          asyncData[fileEntry.toURL()].file = file;
-        });
+        if (!(asyncData[fileEntry.toURL()].file)) {
+          fileEntry.file(function(file) {
+            asyncData[fileEntry.toURL()].file = file;
+          });
+        }
       })(fileEntries[i]);
     }
   }
 
   if (entries.length === 1) {
     // For single selection, the dragged element is created in advance,
     // otherwise an image may not be loaded at the time the 'dragstart' event
     // comes.
     this.preloadThumbnailImage_(entries[0]);
   }
@@ skipping 85 matching lines @@
       listItems.push(listItem);
     }
   }
 
   setTimeout(function() {
     for (var i = 0; i < listItems.length; i++) {
       listItems[i].classList.remove('blink');
     }
   }, 100);
 };