PPAPI: Make blocking completion callbacks work.

ppapi/thunk/ppb_file_chooser_api.h

 // 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_PPB_FILE_CHOOSER_API_H_
 #define PPAPI_THUNK_PPB_FILE_CHOOSER_API_H_
 
 #include "ppapi/c/dev/ppb_file_chooser_dev.h"
+#include "ppapi/shared_impl/api_callback_type.h"
 
 namespace ppapi {
 namespace thunk {
 
 class PPB_FileChooser_API {
  public:
   virtual ~PPB_FileChooser_API() {}
 
   virtual int32_t Show(const PP_ArrayOutput& output,
-                       const PP_CompletionCallback& callback) = 0;
+                       ApiCallbackType callback) = 0;
 
   // Trusted API.
   virtual int32_t ShowWithoutUserGesture(
       PP_Bool save_as,
       PP_Var suggested_file_name,
       const PP_ArrayOutput& output,
-      const PP_CompletionCallback& callback) = 0;
+      ApiCallbackType callback) = 0;
 
   // Version 0.5 API.
-  virtual int32_t Show0_5(const PP_CompletionCallback& callback) = 0;
+  virtual int32_t Show0_5(ApiCallbackType callback) = 0;
   virtual PP_Resource GetNextChosenFile() = 0;
 
   // Trusted version 0.5 API.
   virtual int32_t ShowWithoutUserGesture0_5(
       PP_Bool save_as,
       PP_Var suggested_file_name,
-      const PP_CompletionCallback& callback) = 0;
+      ApiCallbackType callback) = 0;
 };
 
 }  // namespace thunk
 }  // namespace ppapi
 
 #endif  // PPAPI_THUNK_PPB_FILE_CHOOSER_API_H_