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 29 matching lines @@
 
 class UndoStep : public GarbageCollectedFinalized<UndoStep> {
  public:
   virtual ~UndoStep() {}
   DEFINE_INLINE_VIRTUAL_TRACE() {}
 
   virtual bool belongsTo(const LocalFrame&) const = 0;
   virtual void unapply() = 0;
   virtual void reapply() = 0;
   virtual InputEvent::InputType inputType() const = 0;
+  virtual int sequence() const = 0;

[yosin_UTC9, 2017/01/17 08:13:29]

Do we really want to keep |UndoStep| as interface?

I think it is better to have sequence number as const member variable
initialized in ctor.


BTW,
We should get rid of GarbageCollectedFinalized<UndoStep> since it doesn't have
member variables to track.

[Xiaocheng, 2017/01/17 09:04:02]

Do you mean removing |UndoStep| and using |EditCommandComposition| directly? In
fact what's the reason of having |UndoStep|?
Is the construction order of the steps same as the order they are pushed to undo
stack? If so, then yes.

+  virtual void setSequence(int) = 0;
 };
 
 }  // namespace blink
 
 #endif