PPAPI: Force async callback invocation option.

ppapi/thunk/common.h

Index: ppapi/thunk/common.h
===================================================================
--- ppapi/thunk/common.h	(revision 0)
+++ ppapi/thunk/common.h	(revision 0)
@@ -0,0 +1,21 @@
+// 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.
+
+#ifndef PPAPI_THUNK_COMMON_H_
+#define PPAPI_THUNK_COMMON_H_
+
+#include "ppapi/c/pp_completion_callback.h"
+
+namespace ppapi {
+namespace thunk {
+
+// Skips callback invocation and returns |result| if callback function is NULL
+// or PP_COMPLETIONCALLBACK_FLAG_OPTIONAL is set. Otherwise, schedules the
+// callback with |result| as an argument and returns PP_OK_COMPLETIONPENDING.
+int32_t MayForceCallback(PP_CompletionCallback callback, int32_t result);
+
+}  // namespace thunk
+}  // namespace ppapi
+
+#endif  // PPAPI_THUNK_COMMON_H_