Remove the overflowchanged event with a runtime flag

Source/core/events/OverflowEvent.cpp

Index: Source/core/events/OverflowEvent.cpp
diff --git a/Source/core/events/OverflowEvent.cpp b/Source/core/events/OverflowEvent.cpp
index 2f21507a850f750682cfe17176ef0d3cd8e4722f..e25e59b239aca6d4d93b471c5b3f233d81048e5e 100644
--- a/Source/core/events/OverflowEvent.cpp
+++ b/Source/core/events/OverflowEvent.cpp
@@ -26,6 +26,8 @@
 #include "config.h"
 #include "core/events/OverflowEvent.h"
 
+#include "platform/RuntimeEnabledFeatures.h"
+
 namespace blink {
 
 OverflowEvent::OverflowEvent()
@@ -34,6 +36,7 @@ OverflowEvent::OverflowEvent()
     , m_horizontalOverflow(false)
     , m_verticalOverflow(false)
 {
+    ASSERT(RuntimeEnabledFeatures::overflowChangedEventEnabled());
 }
 
 OverflowEvent::OverflowEvent(bool horizontalOverflowChanged, bool horizontalOverflow, bool verticalOverflowChanged, bool verticalOverflow)
@@ -41,6 +44,7 @@ OverflowEvent::OverflowEvent(bool horizontalOverflowChanged, bool horizontalOver
     , m_horizontalOverflow(horizontalOverflow)
     , m_verticalOverflow(verticalOverflow)
 {
+    ASSERT(RuntimeEnabledFeatures::overflowChangedEventEnabled());
     ASSERT(horizontalOverflowChanged || verticalOverflowChanged);
 
     if (horizontalOverflowChanged && verticalOverflowChanged)
@@ -57,6 +61,8 @@ OverflowEvent::OverflowEvent(const AtomicString& type, const OverflowEventInit&
     , m_horizontalOverflow(false)
     , m_verticalOverflow(false)
 {
+    ASSERT(RuntimeEnabledFeatures::overflowChangedEventEnabled());
+
     if (initializer.hasOrient())
         m_orient = initializer.orient();
     if (initializer.hasHorizontalOverflow())