[fsp] Add an information that root entry name should be an empty string

chrome/common/extensions/api/file_system_provider.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.
 
 // Use the <code>chrome.fileSystemProvider</code> API to create file systems,
 // that can be accessible from the file manager on Chrome OS.
 [implemented_in="chrome/browser/chromeos/extensions/file_system_provider/file_system_provider_api.h"]
 namespace fileSystemProvider {
   // Error codes used by providing extensions in response to requests as well
   // as in case of errors when calling methods of the API. For success, <code>
@@ skipping 28 matching lines @@
   enum ChangeType {
     CHANGED,
     DELETED
   };
 
   // Represents metadata of a file or a directory.
   dictionary EntryMetadata {
     // True if it is a directory.
     boolean isDirectory;
 
-    // Name of this entry (not full path name). Must not contain '/'.
+    // Name of this entry (not full path name). Must not contain '/'. For root
+    // it must be empty.
     DOMString name;
 
     // File size in bytes.
     double size;
 
     // The last modified time of this entry.
     [instanceOf=Date] object modificationTime;
 
     // Mime type for the entry.
     DOMString? mimeType;
@@ skipping 570 matching lines @@
 
     // Raised when the watcher should be removed. If an error occurs, then
     // <code>errorCallback</code> must be called.
     [maxListeners=1, nodoc] static void onRemoveWatcherRequested(
       RemoveWatcherRequestedOptions options,
       ProviderSuccessCallback successCallback,
       ProviderErrorCallback errorCallback);
   };
 };