Adding missing forward declaration of struct PP_CompletionCallback....

ppapi/c/dev/ppb_file_ref_dev.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_C_DEV_PPB_FILE_REF_DEV_H_
 #define PPAPI_C_DEV_PPB_FILE_REF_DEV_H_
 
 #include "ppapi/c/dev/pp_file_info_dev.h"
 #include "ppapi/c/pp_bool.h"
 #include "ppapi/c/pp_instance.h"
 #include "ppapi/c/pp_resource.h"
 #include "ppapi/c/pp_var.h"
 
+struct PP_CompletionCallback;
+
 #define PPB_FILEREF_DEV_INTERFACE "PPB_FileRef(Dev);0.7"
 
 // A FileRef is a "weak pointer" to a file in a file system.  It contains a
 // PP_FileSystemType identifier and a file path string.
 struct PPB_FileRef_Dev {
   // Creates a weak pointer to a file in the given filesystem. File paths are
   // POSIX style.  Returns 0 if the path is malformed.
   PP_Resource (*Create)(PP_Resource file_system, const char* path);
 
   // Returns PP_TRUE if the given resource is a FileRef. Returns PP_FALSE if the
@@ skipping 45 matching lines @@
   // Rename a file or directory.  file_ref and new_file_ref must both refer to
   // files in the same filesystem.  It is an error to rename a file or
   // directory that is in use.  It is not valid to rename a file in the
   // external filesystem.
   int32_t (*Rename)(PP_Resource file_ref,
                     PP_Resource new_file_ref,
                     struct PP_CompletionCallback callback);
 };
 
 #endif  /* PPAPI_C_DEV_PPB_FILE_REF_DEV_H_ */
-