PPAPI: Make blocking completion callbacks work.

ppapi/thunk/ppb_file_system_api.h

Index: ppapi/thunk/ppb_file_system_api.h
diff --git a/ppapi/thunk/ppb_file_system_api.h b/ppapi/thunk/ppb_file_system_api.h
index 096d0721235ce473cfb245a7c187111fa0babaf4..f9524dc0fd058aba5cff5d5156f312e4674752a6 100644
--- a/ppapi/thunk/ppb_file_system_api.h
+++ b/ppapi/thunk/ppb_file_system_api.h
@@ -1,13 +1,17 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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_SYSTEM_API_H_
 #define PPAPI_THUNK_PPB_FILE_SYSTEM_API_H_
 
+#include "base/memory/ref_counted.h"
 #include "ppapi/c/ppb_file_system.h"
 
 namespace ppapi {
+
+class TrackedCallback;
+
 namespace thunk {
 
 class PPB_FileSystem_API {
@@ -15,7 +19,7 @@ class PPB_FileSystem_API {
   virtual ~PPB_FileSystem_API() {}
 
   virtual int32_t Open(int64_t expected_size,
-                       PP_CompletionCallback callback) = 0;
+                       scoped_refptr<TrackedCallback> callback) = 0;
   virtual PP_FileSystemType GetType() = 0;
 };