Remove support for the keygen tag

third_party/WebKit/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 645 matching lines @@
     V8UIEvent_InitUIEvent_Method = 873,
     V8Document_CreateTouch_Method = 874,
     RequestFileSystemNonWebbyOrigin = 876,
     V8MemoryInfo_TotalJSHeapSize_AttributeGetter = 879,
     V8MemoryInfo_UsedJSHeapSize_AttributeGetter = 880,
     V8MemoryInfo_JSHeapSizeLimit_AttributeGetter = 881,
     V8Performance_Timing_AttributeGetter = 882,
     V8Performance_Navigation_AttributeGetter = 883,
     V8Performance_Memory_AttributeGetter = 884,
     V8SharedWorker_WorkerStart_AttributeGetter = 885,
-    HTMLKeygenElement = 886,
     // The above items are available in M45 branch.
 
     HTMLMediaElementPreloadNone = 892,
     HTMLMediaElementPreloadMetadata = 893,
     HTMLMediaElementPreloadAuto = 894,
     HTMLMediaElementPreloadDefault = 895,
     MixedContentBlockableAllowed = 896,
     PseudoBeforeAfterForInputElement = 897,
     V8Permissions_Revoke_Method = 898,
     LinkRelDnsPrefetch = 899,
@@ skipping 779 matching lines @@
     // Tracks what features/properties need to be reported to the legacy
     // histograms.
     BitVector m_featureBits;
     BitVector m_CSSBits;
   } m_legacyCounter;
 };
 
 }  // namespace blink
 
 #endif  // UseCounter_h