Add sequence number to undo steps

third_party/WebKit/Source/core/editing/commands/UndoStep.h

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 47 matching lines @@
   const VisibleSelection& endingSelection() const { return m_endingSelection; }
   void setStartingSelection(const VisibleSelection&);
   void setEndingSelection(const VisibleSelection&);
   Element* startingRootEditableElement() const {
     return m_startingRootEditableElement.get();
   }
   Element* endingRootEditableElement() const {
     return m_endingRootEditableElement.get();
   }
 
+  uint64_t sequenceNumber() const { return m_sequenceNumber; }
+
   DECLARE_TRACE();
 
  private:
   UndoStep(Document*,
            const VisibleSelection& startingSelection,
            const VisibleSelection& endingSelection,
            InputEvent::InputType);
 
   Member<Document> m_document;
   VisibleSelection m_startingSelection;
   VisibleSelection m_endingSelection;
   HeapVector<Member<SimpleEditCommand>> m_commands;
   Member<Element> m_startingRootEditableElement;
   Member<Element> m_endingRootEditableElement;
   InputEvent::InputType m_inputType;
+  const uint64_t m_sequenceNumber;
 };
 
 }  // namespace blink
 
 #endif