Add QuicStrCat.

net/quic/core/quic_connection_test.cc

 // Copyright (c) 2012 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/quic/core/quic_connection.h"
 
 #include <errno.h>
 #include <memory>
 #include <ostream>
 #include <utility>
@@ skipping 1132 matching lines @@
 
   QuicStreamFrame stream_frame(1u, false, 0u, StringPiece());
   EXPECT_CALL(visitor_, OnStreamFrame(_)).Times(3);
   QuicIpAddress host;
   host.FromString("1.1.1.1");
   QuicSocketAddress self_address1(host, 443);
   ProcessFramePacketWithAddresses(QuicFrame(&stream_frame), self_address1,
                                   kPeerAddress);
   // Cause self_address change to mapped Ipv4 address.
   QuicIpAddress host2;
-  host2.FromString(base::StringPrintf(
-      "::ffff:%s", connection_.self_address().host().ToString().c_str()));
+  host2.FromString(
+      QuicStrCat("::ffff:", connection_.self_address().host().ToString()));
   QuicSocketAddress self_address2(host2, connection_.self_address().port());
   ProcessFramePacketWithAddresses(QuicFrame(&stream_frame), self_address2,
                                   kPeerAddress);
   EXPECT_TRUE(connection_.connected());
   // self_address change back to Ipv4 address.
   ProcessFramePacketWithAddresses(QuicFrame(&stream_frame), self_address1,
                                   kPeerAddress);
   EXPECT_TRUE(connection_.connected());
 }
 
@@ skipping 3953 matching lines @@
                             error_details, ConnectionCloseSource::FROM_PEER));
   connection_.set_perspective(Perspective::IS_CLIENT);
   connection_.CloseConnection(QUIC_CRYPTO_HANDSHAKE_STATELESS_REJECT,
                               error_details,
                               ConnectionCloseBehavior::SILENT_CLOSE);
 }
 
 }  // namespace
 }  // namespace test
 }  // namespace net