PPAPI: Force async callback invocation option.

ppapi/cpp/dev/file_system_dev.cc

-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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.
 
 #include "ppapi/cpp/dev/file_system_dev.h"
 
 #include "ppapi/c/dev/ppb_file_system_dev.h"
 #include "ppapi/c/pp_errors.h"
 #include "ppapi/cpp/completion_callback.h"
 #include "ppapi/cpp/dev/file_ref_dev.h"
 #include "ppapi/cpp/module.h"
@@ skipping 13 matching lines @@
                                PP_FileSystemType_Dev type) {
   if (!has_interface<PPB_FileSystem_Dev>())
     return;
   PassRefFromConstructor(get_interface<PPB_FileSystem_Dev>()->Create(
       instance->pp_instance(), type));
 }
 
 int32_t FileSystem_Dev::Open(int64_t expected_size,
                              const CompletionCallback& cc) {
   if (!has_interface<PPB_FileSystem_Dev>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_FileSystem_Dev>()->Open(
       pp_resource(), expected_size, cc.pp_completion_callback());
 }
 
 }  // namespace pp