[fsp] Let extensions decide about the file system id.

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 216 matching lines @@
 
   // Image set of profile image.
   ImageSet? profileImage;
 };
 
 // Mounted disk volume metadata.
 dictionary VolumeMetadata {
   // ID of the disk volume.
   DOMString volumeId;
 
+  // Id the provided file system (for proviided file systems).
+  DOMString? fileSystemId;
+
   // Extension providing this volume (for provided file systems).
   DOMString? extensionId;
 
   // Label of the volume (if available).
   DOMString? volumeLabel;
 
   // Description of the profile where the volume belongs.
   // TODO(hirono): Remove the property because of the design change of
   // multi-profile support.
   ProfileInfo profile;
@@ skipping 531 matching lines @@
   static void onDriveSyncError(DriveSyncErrorEvent event);
 
   // Dispatched when a profile is added.
   static void onProfileAdded();
 
   // Dispatched when any window moves another desktop.
   // TODO(hirono): Add information which window is moved.
   static void onDesktopChanged();
 };
 };