Files.app: Add private API to check if PiexLoader is enabled or not.

chrome/common/extensions/api/file_manager_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.
 
 // fileManagerPrivate API.
 // This is a private API used by the file browser of ChromeOS.
 [platforms=("chromeos"),
  implemented_in="chrome/browser/chromeos/extensions/file_manager/file_manager_private_api_functions.h"]
 namespace fileManagerPrivate {
 // Type of the mounted volume.
@@ skipping 854 matching lines @@
 
   // Is UMA enabled?
   static void isUMAEnabled(BooleanCallback callback);
 
   // Sets a tag on a file or a directory. Only Drive files are supported.
   static void setEntryTag(DOMString entryURL,
                           EntryTagVisibility visibility,
                           DOMString key,
                           DOMString value,
                           SimpleCallback callback);
+
+  // Returns if Piex loader is enabled.
+  static void isPiexLoaderEnabled(BooleanCallback callback);
 };
 
 interface Events {
   static void onMountCompleted(MountCompletedEvent 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);
 };
 };