Add sequence number to undo steps

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

Index: third_party/WebKit/Source/core/editing/commands/UndoStep.h
diff --git a/third_party/WebKit/Source/core/editing/commands/UndoStep.h b/third_party/WebKit/Source/core/editing/commands/UndoStep.h
index c0e1935eb3f2bc0a27e8b52c84dbd9b2c710ecde..56aa7fc3968a184d1cc86b46d02d33747659beb0 100644
--- a/third_party/WebKit/Source/core/editing/commands/UndoStep.h
+++ b/third_party/WebKit/Source/core/editing/commands/UndoStep.h
@@ -65,6 +65,9 @@ class UndoStep : public GarbageCollectedFinalized<UndoStep> {
     return m_endingRootEditableElement.get();
   }
 
+  uint64_t sequence() const { return m_sequence; }

[yosin_UTC9, 2017/01/19 06:40:52]

s/sequence/sequenceNumber()/

Term "sequence" is ambiguous, it can be list, array, etc.

[Xiaocheng, 2017/01/19 07:52:30]

Will do.

+  void setSequence(uint64_t passedSequence) { m_sequence = passedSequence; }
+
   DECLARE_TRACE();
 
  private:
@@ -80,6 +83,7 @@ class UndoStep : public GarbageCollectedFinalized<UndoStep> {
   Member<Element> m_startingRootEditableElement;
   Member<Element> m_endingRootEditableElement;
   InputEvent::InputType m_inputType;
+  uint64_t m_sequence;

[yosin_UTC9, 2017/01/19 06:40:52]

Can we make |const unit64_t m_sequenceNumber| and initialized in constructor?
I fill changing sequence number is some what strange since usually sequence
number is used for object identifier.

[Xiaocheng, 2017/01/19 07:52:30]

For undo steps, is the creation order same as the push-to-undo-stack order? We
can initialize the sequence number only if this is true.

 };
 
 }  // namespace blink