Removing x-x509-user-cert mime handler.

components/mime_util/mime_util.h

 // Copyright 2015 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.
 
 #ifndef COMPONENTS_MIME_UTIL_MIME_UTIL_H__
 #define COMPONENTS_MIME_UTIL_MIME_UTIL_H__
 
 #include <string>
 
 #include "net/base/mime_util.h"
 
 namespace mime_util {
 
 // Check to see if a particular MIME type is in the list of
 // supported/recognized MIME types.
 bool IsSupportedImageMimeType(const std::string& mime_type);
 bool IsSupportedNonImageMimeType(const std::string& mime_type);
 bool IsUnsupportedTextMimeType(const std::string& mime_type);
 bool IsSupportedJavascriptMimeType(const std::string& mime_type);
-bool IsSupportedCertificateMimeType(const std::string& mime_type);
 
 // Convenience function.
 bool IsSupportedMimeType(const std::string& mime_type);
 
 net::CertificateMimeType GetCertificateMimeTypeForMimeType(
     const std::string& mime_type);
 
 }  // namespace mime_util
 
 #endif  // COMPONENTS_MIME_UTIL_MIME_UTIL_H__