Convert more interfaces to the new thunk system.

ppapi/thunk/ppb_file_system_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_SYSTEM_API_H_
+#define PPAPI_THUNK_PPB_FILE_SYSTEM_API_H_
+
+#include "ppapi/c/dev/ppb_file_system_dev.h"
+
+namespace ppapi {
+namespace thunk {
+
+class PPB_FileSystem_API {
+ public:
+  virtual int32_t Open(int64_t expected_size,
+                       PP_CompletionCallback callback) = 0;
+  virtual PP_FileSystemType_Dev GetType() = 0;
+};
+
+}  // namespace thunk
+}  // namespace ppapi
+
+#endif  // PPAPI_THUNK_PPB_FILE_SYSTEM_API_H_