Remove support for the keygen tag

third_party/WebKit/Source/core/frame/Deprecation.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/frame/Deprecation.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/ExecutionContext.h"
 #include "core/frame/FrameConsole.h"
 #include "core/frame/FrameHost.h"
@@ skipping 351 matching lines @@
                         "'Performance.clearResourceTimings'");
 
     case UseCounter::PrefixedPerformanceSetResourceTimingBufferSize:
       return replacedBy("'Performance.webkitSetResourceTimingBufferSize'",
                         "'Performance.setResourceTimingBufferSize'");
 
     case UseCounter::PrefixedPerformanceResourceTimingBufferFull:
       return replacedBy("'Performance.onwebkitresourcetimingbufferfull'",
                         "'Performance.onresourcetimingbufferfull'");
 
-    case UseCounter::HTMLKeygenElement:
-      return willBeRemoved("The <keygen> element", M57, "5716060992962560");
-
     case UseCounter::EncryptedMediaAllSelectedContentTypesMissingCodecs:
       return String::format(
           "EME requires that contentType strings accepted by "
           "requestMediaKeySystemAccess() include codecs. Non-standard support "
           "for contentType strings without codecs will be removed in %s. "
           "Please specify the desired codec(s) as part of the contentType.",
           milestoneString(M58));
 
     case UseCounter::EncryptedMediaCapabilityNotProvided:
       return String::format(
@@ skipping 24 matching lines @@
           "redirected response. This will result in an error in %s.",
           milestoneString(M59));
 
     // Features that aren't deprecated don't have a deprecation message.
     default:
       return String();
   }
 }
 
 }  // namespace blink