Revert of Move UndoStack from Page to Editor

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

Index: third_party/WebKit/Source/core/editing/commands/UndoStack.h
diff --git a/third_party/WebKit/Source/core/editing/commands/UndoStack.h b/third_party/WebKit/Source/core/editing/commands/UndoStack.h
index 50ac9a5de29e44dd067467244773fc2c2db3ee31..39615d15d3bac4c46217529dc1f7faf8130ace83 100644
--- a/third_party/WebKit/Source/core/editing/commands/UndoStack.h
+++ b/third_party/WebKit/Source/core/editing/commands/UndoStack.h
@@ -40,8 +40,6 @@
 class LocalFrame;
 class UndoStep;
 
-// |UndoStack| is owned by and always 1:1 to |Editor|. Since |Editor| is 1:1 to
-// |LocalFrame|, |UndoStack| is also 1:1 to |LocalFrame|.
 class UndoStack final : public GarbageCollected<UndoStack> {
     WTF_MAKE_NONCOPYABLE(UndoStack);
 public:
@@ -49,6 +47,7 @@
 
     void registerUndoStep(UndoStep*);
     void registerRedoStep(UndoStep*);
+    void didUnloadFrame(const LocalFrame&);
     bool canUndo() const;
     bool canRedo() const;
     void undo();
@@ -61,6 +60,8 @@
 
     typedef HeapDeque<Member<UndoStep>> UndoStepStack;
 
+    void filterOutUndoSteps(UndoStepStack&, const LocalFrame&);
+
     bool m_inRedo;
     UndoStepStack m_undoStack;
     UndoStepStack m_redoStack;