Remove the (already disabled) OverflowChangedEvent runtime flag

Source/core/frame/UseCounter.h

 /*
  * Copyright (C) 2012 Google, Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 194 matching lines @@
         InputTypePassword = 192,
         InputTypePasswordMaxLength = 193,
         PrefixedPageVisibility = 196,
         CSSStyleSheetInsertRuleOptionalArg = 198, // Inconsistent with the specification and other browsers.
         DocumentBeforeUnloadRegistered = 200,
         DocumentBeforeUnloadFired = 201,
         DocumentUnloadRegistered = 202,
         DocumentUnloadFired = 203,
         SVGLocatableNearestViewportElement = 204,
         SVGLocatableFarthestViewportElement = 205,
-        OverflowChangedEvent = 208,
         SVGPointMatrixTransform = 209,
         DOMFocusInOutEvent = 211,
         FileGetLastModifiedDate = 212,
         HTMLElementInnerText = 213,
         HTMLElementOuterText = 214,
         ReplaceDocumentViaJavaScriptURL = 215,
         ElementSetAttributeNodeNS = 216,
         ElementPrefixedMatchesSelector = 217,
         CSSStyleSheetRules = 219,
         CSSStyleSheetAddRule = 220,
@@ skipping 642 matching lines @@
 
     bool hasRecordedMeasurement(Feature feature) const { return m_countBits.hasRecordedMeasurement(feature); }
 
     CountBits m_countBits;
     BitVector m_CSSFeatureBits;
 };
 
 } // namespace blink
 
 #endif // UseCounter_h