Add virtual destructors for the Pepper API thunks.

ppapi/thunk/ppb_file_io_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_IO_API_H_
 #define PPAPI_THUNK_PPB_FILE_IO_API_H_
 
 #include "ppapi/c/dev/ppb_file_io_dev.h"
 
 namespace ppapi {
 namespace thunk {
 
 class PPB_FileIO_API {
  public:
+  virtual ~PPB_FileIO_API() {}
+
   virtual int32_t Open(PP_Resource file_ref,
                        int32_t open_flags,
                        PP_CompletionCallback callback) = 0;
   virtual int32_t Query(PP_FileInfo_Dev* info,
                         PP_CompletionCallback callback) = 0;
   virtual int32_t Touch(PP_Time last_access_time,
                         PP_Time last_modified_time,
                         PP_CompletionCallback callback) = 0;
   virtual int32_t Read(int64_t offset,
                        char* buffer,
@@ skipping 14 matching lines @@
                             int32_t bytes_to_write,
                             PP_CompletionCallback callback) = 0;
   virtual int32_t WillSetLength(int64_t length,
                                 PP_CompletionCallback callback) = 0;
 };
 
 }  // namespace thunk
 }  // namespace ppapi
 
 #endif  // PPAPI_THUNK_PPB_FILE_IO_API_H_