Remove unused function UndoStep::belongsTo()

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 4aa768978e4bf149ce539dc85ebfd7fdee6d256e..9ee7497a345c1ee6198fe887ad1d66d1bd091113 100644
--- a/third_party/WebKit/Source/core/editing/commands/UndoStep.h
+++ b/third_party/WebKit/Source/core/editing/commands/UndoStep.h
@@ -36,14 +36,11 @@
 
 namespace blink {
 
-class LocalFrame;
-
 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;