Add sequence number to undo steps

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

Index: third_party/WebKit/Source/core/editing/commands/UndoStep.cpp
diff --git a/third_party/WebKit/Source/core/editing/commands/UndoStep.cpp b/third_party/WebKit/Source/core/editing/commands/UndoStep.cpp
index bbc47d2ad5d3750119842c5ce9b93e9867679904..837955ea8e8f9928fb78b2ee5fc161135c25c969 100644
--- a/third_party/WebKit/Source/core/editing/commands/UndoStep.cpp
+++ b/third_party/WebKit/Source/core/editing/commands/UndoStep.cpp
@@ -9,6 +9,11 @@
 
 namespace blink {
 
+namespace {
+

[yosin_UTC9, 2017/02/20 06:17:50]

nit: Get rid this extra blank line or add a blank before L15.

[Xiaocheng, 2017/02/22 02:47:32]

|git cl format| did this.

I'll remove the blank line.

+uint64_t s_nextSequenceNumber = 0;

[yosin_UTC9, 2017/02/20 06:17:50]

nit:s/nextSequneceNumber/currentSequenceNumber/
Since, we do pre-increment.

The another way is

uint64_t nextSequenceNumbr() {
  static uint64_t currentSequenceNumber = 0;
  return ++currentSequenceNumber;
}

This is more encapsulating management of sequence number.

[Xiaocheng, 2017/02/22 02:47:32]

Done.
This appears to me as introducing unnecessary complexity...

+}
+
 UndoStep* UndoStep::create(Document* document,
                            const VisibleSelection& startingSelection,
                            const VisibleSelection& endingSelection,
@@ -25,7 +30,8 @@ UndoStep::UndoStep(Document* document,
       m_endingSelection(endingSelection),
       m_startingRootEditableElement(startingSelection.rootEditableElement()),
       m_endingRootEditableElement(endingSelection.rootEditableElement()),
-      m_inputType(inputType) {}
+      m_inputType(inputType),
+      m_sequenceNumber(++s_nextSequenceNumber) {}
 
 void UndoStep::unapply() {
   DCHECK(m_document);