PPAPI: Force async callback invocation option.

ppapi/cpp/graphics_2d.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/graphics_2d.h"
 
 #include "ppapi/c/pp_errors.h"
 #include "ppapi/c/ppb_graphics_2d.h"
 #include "ppapi/cpp/common.h"
 #include "ppapi/cpp/completion_callback.h"
 #include "ppapi/cpp/image_data.h"
@@ skipping 81 matching lines @@
   get_interface<PPB_Graphics2D>()->ReplaceContents(pp_resource(),
                                                    image->pp_resource());
 
   // On success, reset the image data. This is to help prevent people
   // from continuing to use the resource which will result in artifacts.
   *image = ImageData();
 }
 
 int32_t Graphics2D::Flush(const CompletionCallback& cc) {
   if (!has_interface<PPB_Graphics2D>())
-    return PP_ERROR_NOINTERFACE;
+    return cc.MayForce(PP_ERROR_NOINTERFACE);
   return get_interface<PPB_Graphics2D>()->Flush(pp_resource(),
                                                 cc.pp_completion_callback());
 }
 
 }  // namespace pp