Add ChaCha20Poly1305Encrypter, based on

net/quic/crypto/chacha20_poly1305_decrypter.h

+// Copyright (c) 2013 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_QUIC_CRYPTO_CHACHA20_POLY1305_DECRYPTER_H_
+#define NET_QUIC_CRYPTO_CHACHA20_POLY1305_DECRYPTER_H_
+
+#include "net/quic/crypto/aead_base_decrypter.h"
+
+namespace net {
+
+// A ChaCha20Poly1305Decrypter is a QuicDecrypter that implements the
+// AEAD_CHACHA20_POLY1305 algorithm specified in
+// draft-agl-tls-chacha20poly1305-04. Create an instance by calling
+// QuicDecrypter::Create(kCC12).
+//
+// It uses an authentication tag of 16 bytes (128 bits). There is no
+// fixed nonce prefix.
+class NET_EXPORT_PRIVATE ChaCha20Poly1305Decrypter : public AeadBaseDecrypter {
+ public:
+  enum {
+    kAuthTagSize = 16,
+  };
+
+  ChaCha20Poly1305Decrypter();
+  virtual ~ChaCha20Poly1305Decrypter();
+
+  // Returns true if the underlying crypto library supports ChaCha20+Poly1305.
+  static bool IsSupported();
+
+#if !defined(USE_OPENSSL)
+ protected:
+  // AeadBaseDecrypter methods:
+  virtual void FillAeadParams(base::StringPiece nonce,
+                              base::StringPiece associated_data,
+                              size_t auth_tag_size,
+                              AeadParams* aead_params) const OVERRIDE;
+#endif
+};
+
+}  // namespace net
+
+#endif  // NET_QUIC_CRYPTO_CHACHA20_POLY1305_DECRYPTER_H_