Add QuicStrCat.

net/quic/core/quic_crypto_client_stream.cc

Index: net/quic/core/quic_crypto_client_stream.cc
diff --git a/net/quic/core/quic_crypto_client_stream.cc b/net/quic/core/quic_crypto_client_stream.cc
index 98a64abafd8c8fd156b7784bc80f8e00e297bb26..9d1b18abdafe1144f4958afb6161f1b17fd327e6 100644
--- a/net/quic/core/quic_crypto_client_stream.cc
+++ b/net/quic/core/quic_crypto_client_stream.cc
@@ -22,6 +22,8 @@ using std::string;
 
 namespace net {
 
+const int QuicCryptoClientStream::kMaxClientHellos;
+
 QuicCryptoClientStreamBase::QuicCryptoClientStreamBase(QuicSession* session)
     : QuicCryptoStream(session) {}
 
@@ -277,7 +279,7 @@ void QuicCryptoClientStream::DoSendCHLO(
   if (num_client_hellos_ > kMaxClientHellos) {
     CloseConnectionWithDetails(
         QUIC_CRYPTO_TOO_MANY_REJECTS,
-        base::StringPrintf("More than %u rejects", kMaxClientHellos).c_str());
+        QuicStrCat("More than ", kMaxClientHellos, " rejects"));
     return;
   }
   num_client_hellos_++;