Remove support for the keygen tag

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

Index: third_party/WebKit/Source/core/frame/Deprecation.cpp
diff --git a/third_party/WebKit/Source/core/frame/Deprecation.cpp b/third_party/WebKit/Source/core/frame/Deprecation.cpp
index 6284adb2f49a04c4558cb2123b68384e1e86d812..b9f35a0ddb52277ff202eddc90f1bae96698def4 100644
--- a/third_party/WebKit/Source/core/frame/Deprecation.cpp
+++ b/third_party/WebKit/Source/core/frame/Deprecation.cpp
@@ -388,9 +388,6 @@ String Deprecation::deprecationMessage(UseCounter::Feature feature) {
       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 "