Remove the overflowchanged event with a runtime flag

Source/core/events/OverflowEvent.cpp

 /*
  * Copyright (C) 2006, 2007 Apple Inc. All rights reserved.
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 #include "config.h"
 #include "core/events/OverflowEvent.h"
 
+#include "platform/RuntimeEnabledFeatures.h"
+
 namespace blink {
 
 OverflowEvent::OverflowEvent()
     : Event(EventTypeNames::overflowchanged, false, false)
     , m_orient(VERTICAL)
     , m_horizontalOverflow(false)
     , m_verticalOverflow(false)
 {
+    ASSERT(RuntimeEnabledFeatures::overflowChangedEventEnabled());
 }
 
 OverflowEvent::OverflowEvent(bool horizontalOverflowChanged, bool horizontalOverflow, bool verticalOverflowChanged, bool verticalOverflow)
     : Event(EventTypeNames::overflowchanged, false, false)
     , m_horizontalOverflow(horizontalOverflow)
     , m_verticalOverflow(verticalOverflow)
 {
+    ASSERT(RuntimeEnabledFeatures::overflowChangedEventEnabled());
     ASSERT(horizontalOverflowChanged || verticalOverflowChanged);
 
     if (horizontalOverflowChanged && verticalOverflowChanged)
         m_orient = BOTH;
     else if (horizontalOverflowChanged)
         m_orient = HORIZONTAL;
     else
         m_orient = VERTICAL;
 }
 
 OverflowEvent::OverflowEvent(const AtomicString& type, const OverflowEventInit& initializer)
     : Event(type, initializer)
     , m_orient(0)
     , m_horizontalOverflow(false)
     , m_verticalOverflow(false)
 {
+    ASSERT(RuntimeEnabledFeatures::overflowChangedEventEnabled());
+
     if (initializer.hasOrient())
         m_orient = initializer.orient();
     if (initializer.hasHorizontalOverflow())
         m_horizontalOverflow = initializer.horizontalOverflow();
     if (initializer.hasVerticalOverflow())
         m_verticalOverflow = initializer.verticalOverflow();
 }
 
 const AtomicString& OverflowEvent::interfaceName() const
 {
     return EventNames::OverflowEvent;
 }
 
 DEFINE_TRACE(OverflowEvent)
 {
     Event::trace(visitor);
 }
 
 }