Mac: implement <keygen> support, including adding generated cert to the Keychain.

net/base/keygen_handler_win.cc

 // Copyright (c) 2009 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 "net/base/keygen_handler.h"
 
 #include "base/logging.h"
 
 namespace net {
 
-KeygenHandler::KeygenHandler(int key_size_index,
-                             const std::string& challenge)
-    : key_size_index_(key_size_index),
-      challenge_(challenge) {
-  NOTIMPLEMENTED();
-}
-
 std::string KeygenHandler::GenKeyAndSignChallenge() {
   NOTIMPLEMENTED();
   return std::string();
 }
 
 }  // namespace net