Unwind fallback metrics and SSLFailureState.

net/ssl/ssl_failure_state.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 NET_SSL_SSL_FAILURE_STATE_H_
-#define NET_SSL_SSL_FAILURE_STATE_H_
-
-namespace net {
-
-// Describes the most likely cause for the TLS handshake failure. This is an
-// approximation used to classify the causes of TLS version fallback. These
-// values are used in histograms, so new values must be appended.
-enum SSLFailureState {
-  // The connection was successful.
-  SSL_FAILURE_NONE = 0,
-
-  // The connection failed for unknown reasons.
-  SSL_FAILURE_UNKNOWN = 1,
-
-  // The connection failed after sending ClientHello and before receiving
-  // ServerHello.
-  SSL_FAILURE_CLIENT_HELLO = 2,
-
-  // The connection failed after negotiating TLS_RSA_WITH_AES_128_GCM_SHA256 or
-  // TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 and completing the client's second
-  // leg. Some Microsoft IIS servers fail at this point. See
-  // https://crbug.com/433406.
-  SSL_FAILURE_BUGGY_GCM = 3,
-
-  // The connection failed after CertificateVerify was sent. Some servers are
-  // known to incorrectly implement TLS 1.2 client auth.
-  SSL_FAILURE_CLIENT_AUTH = 4,
-
-  // The connection failed because the server attempted to resume a session at
-  // the wrong version. Some versions of OpenSSL may do this in rare
-  // circumstances. See https://crbug.com/441456
-  SSL_FAILURE_SESSION_MISMATCH = 5,
-
-  // The connection failed after sending the NextProto message. Some F5 servers
-  // fail to parse such messages in TLS 1.1 and TLS 1.2, but not 1.0. See
-  // https://crbug.com/466977.
-  SSL_FAILURE_NEXT_PROTO = 6,
-
-  SSL_FAILURE_MAX,
-};
-
-}  // namespace net
-
-#endif  // NET_SSL_SSL_FAILURE_STATE_H_