Add GetSequenceNumber function to PPB_Flash_Clipboard

ppapi/cpp/private/flash_clipboard.h

 // 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_CPP_PRIVATE_FLASH_CLIPBOARD_H_
 #define PPAPI_CPP_PRIVATE_FLASH_CLIPBOARD_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 27 matching lines @@
                        PP_Flash_Clipboard_Type clipboard_type,
                        uint32_t clipboard_format,
                        Var* out);
 
   // Returns true on success in which case all of |data| will be written to
   // the clipboard. Otherwise nothing will be written.
   static bool WriteData(const InstanceHandle& instance,
                         PP_Flash_Clipboard_Type clipboard_type,
                         const std::vector<uint32_t>& formats,
                         const std::vector<Var>& data_items);
+
+  // Outputs a sequence number that uniquely identifies the clipboard state in
+  // |sequence_number| and returns true if successful.
+  static bool GetSequenceNumber(const InstanceHandle& instance,
+                                PP_Flash_Clipboard_Type clipboard_type,
+                                uint64_t* sequence_number);
 };
 
 }  // namespace flash
 }  // namespace pp
 
 #endif  // PPAPI_CPP_PRIVATE_FLASH_CLIPBOARD_H_