Don't crash browser process when OK passed as error code in FSP API.

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,
@@ skipping 500 matching lines @@
   // Callback to receive the result of $(ref:getAll) function.
   callback GetAllCallback = void(FileSystemInfo[] fileSystems);
 
   // Callback to receive the result of $(ref:get) function.
   callback GetCallback = void(FileSystemInfo fileSystem);
 
   // Callback to be called by the providing extension in case of a success.
   [nocompile] callback ProviderSuccessCallback = void();
 
   // Callback to be called by the providing extension in case of an error.
+  // Any error code is allowed except <code>OK</code>.
   [nocompile] callback ProviderErrorCallback = void(ProviderError error);
 
   // Success callback for the $(ref:onGetMetadataRequested) event.
   [nocompile] callback MetadataCallback = void(EntryMetadata metadata);
 
   // Success callback for the $(ref:onGetActionsRequested) event.
   [nocompile] callback ActionsCallback = void(Action[] actions);
 
   // Success callback for the $(ref:onReadDirectoryRequested) event. If more
   // entries will be returned, then <code>hasMore</code> must be true, and it
@@ skipping 243 matching lines @@
     // Raised when executing an action for a set of files or directories is\
     // requested. After the action is completed, <code>successCallback</code>
     // must be called. On error, <code>errorCallback</code> must be called.
     [maxListeners=1] static void onExecuteActionRequested(
       ExecuteActionRequestedOptions options,
       ProviderSuccessCallback successCallback,
       ProviderErrorCallback errorCallback);
   };
 };