Remove support for the keygen tag

third_party/WebKit/Source/core/html/BUILD.gn

 # 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.
 
 import("//build/split_static_library.gni")
 import("//third_party/WebKit/Source/core/core.gni")
 
 blink_core_sources("html") {
   split_count = 5
 
@@ skipping 76 matching lines @@
     "HTMLIFrameElementPermissions.h",
     "HTMLIFrameElementSandbox.cpp",
     "HTMLIFrameElementSandbox.h",
     "HTMLImageElement.cpp",
     "HTMLImageElement.h",
     "HTMLImageFallbackHelper.cpp",
     "HTMLImageFallbackHelper.h",
     "HTMLImageLoader.cpp",
     "HTMLImageLoader.h",
     "HTMLInputElement.cpp",
-    "HTMLKeygenElement.cpp",
-    "HTMLKeygenElement.h",
     "HTMLLIElement.cpp",
     "HTMLLIElement.h",
     "HTMLLabelElement.cpp",
     "HTMLLabelElement.h",
     "HTMLLegendElement.cpp",
     "HTMLLegendElement.h",
     "HTMLLinkElement.cpp",
     "HTMLLinkElement.h",
     "HTMLMapElement.cpp",
     "HTMLMapElement.h",
@@ skipping 402 matching lines @@
     "track/vtt/VTTToken.h",
     "track/vtt/VTTTokenizer.cpp",
     "track/vtt/VTTTokenizer.h",
   ]
 
   configs += [
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     "//build/config/compiler:no_size_t_to_int_warning",
   ]
 }