Make onFileTransferUpdated single value from list.

chrome/common/extensions/api/file_browser_private.idl

 // Copyright 2013 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.
 
 // fileBrowserPrivate API.
 // This is a private API used by the file browser of ChromeOS.
 [platforms=("chromeos"),
  implemented_in="chrome/browser/chromeos/extensions/file_manager/file_browser_private_api_functions.h"]
 namespace fileBrowserPrivate {
 // Type of the mounted volume.
@@ skipping 790 matching lines @@
                            optional SimpleCallback callback);
 
   // Opens inspector window.
   // |type| InspectionType which specifies how to open inspector.
   static void openInspector(InspectionType type);
 };
 
 interface Events {
   static void onMountCompleted(MountCompletedEvent event);
 
-  static void onFileTransfersUpdated(FileTransferStatus[] event);
+  static void onFileTransfersUpdated(FileTransferStatus event);
 
   static void onCopyProgress(long copyId, CopyProgressStatus status);
 
   static void onDirectoryChanged(FileWatchEvent event);
 
   static void onPreferencesChanged();
 
   static void onDriveConnectionStatusChanged();
 
   static void onDeviceChanged(DeviceEvent event);
 
   static void onDriveSyncError(DriveSyncErrorEvent event);
 };
 };