Reland of "Move UndoStack from Page to Editor"

third_party/WebKit/Source/core/editing/Editor.h

Index: third_party/WebKit/Source/core/editing/Editor.h
diff --git a/third_party/WebKit/Source/core/editing/Editor.h b/third_party/WebKit/Source/core/editing/Editor.h
index e2bd766a26d295c6f3010f3a02cfe89e87d24b9d..93ecc72ce88abf60107cfe065368cbbec2587b1c 100644
--- a/third_party/WebKit/Source/core/editing/Editor.h
+++ b/third_party/WebKit/Source/core/editing/Editor.h
@@ -175,6 +175,7 @@ public:
     void undo();
     bool canRedo();
     void redo();
+    void clearUndoStack();
 
     void setBaseWritingDirection(WritingDirection);
 
@@ -253,6 +254,7 @@ public:
 private:
     Member<LocalFrame> m_frame;
     Member<CompositeEditCommand> m_lastEditCommand;
+    const Member<UndoStack> m_undoStack;
     int m_preventRevealSelection;
     bool m_shouldStartNewKillRingSequence;
     bool m_shouldStyleWithCSS;
@@ -273,8 +275,6 @@ private:
     bool canDeleteRange(const EphemeralRange&) const;
     bool shouldDeleteRange(const EphemeralRange&) const;
 
-    UndoStack* undoStack() const;
-
     bool tryDHTMLCopy();
     bool tryDHTMLCut();
     bool tryDHTMLPaste(PasteMode);