Add ChaCha20Poly1305Encrypter, based on

net/quic/crypto/chacha20_poly1305_encrypter_openssl.cc

+// Copyright (c) 2013 The Chromium Authors. All rights reserved.

[agl, 2014/03/10 15:08:33]

Note that the copyright year for the new files is all 2013.

[wtc, 2014/03/11 04:02:02]

I should have annotated this. I noticed that the commit bot automatically fixes
this line when it adds a new file, including whether "(c)" should be used. So I
know I don't need to get this right.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "net/quic/crypto/chacha20_poly1305_encrypter.h"
+
+#include <openssl/evp.h>
+
+namespace net {
+
+namespace {
+
+const size_t kKeySize = 32;
+const size_t kNoncePrefixSize = 0;
+
+}  // namespace
+
+ChaCha20Poly1305Encrypter::ChaCha20Poly1305Encrypter()
+    : AeadBaseEncrypter(EVP_aead_chacha20_poly1305(), kKeySize, kAuthTagSize,
+                        kNoncePrefixSize) {
+  COMPILE_ASSERT(kKeySize <= kMaxKeySize, key_size_too_big);
+  COMPILE_ASSERT(kNoncePrefixSize <= kMaxNoncePrefixSize,
+                 nonce_prefix_size_too_big);
+}
+
+ChaCha20Poly1305Encrypter::~ChaCha20Poly1305Encrypter() {}
+
+// static
+bool ChaCha20Poly1305Encrypter::IsSupported() { return true; }
+
+}  // namespace net