Deprecate --quic_include_path_id_in_iv.

net/quic/crypto/aead_base_decrypter_openssl.cc

Index: net/quic/crypto/aead_base_decrypter_openssl.cc
diff --git a/net/quic/crypto/aead_base_decrypter_openssl.cc b/net/quic/crypto/aead_base_decrypter_openssl.cc
index 097cb4fd5ca4687395089c6c1ec802716d2819e3..cb91a6906d6c55834dac9786a695b3cd22429d86 100644
--- a/net/quic/crypto/aead_base_decrypter_openssl.cc
+++ b/net/quic/crypto/aead_base_decrypter_openssl.cc
@@ -93,14 +93,10 @@ bool AeadBaseDecrypter::DecryptPacket(QuicPathId path_id,
   uint8_t nonce[sizeof(nonce_prefix_) + sizeof(packet_number)];
   const size_t nonce_size = nonce_prefix_size_ + sizeof(packet_number);
   memcpy(nonce, nonce_prefix_, nonce_prefix_size_);
-  if (FLAGS_quic_include_path_id_in_iv) {
-    uint64_t path_id_packet_number =
-        QuicUtils::PackPathIdAndPacketNumber(path_id, packet_number);
-    memcpy(nonce + nonce_prefix_size_, &path_id_packet_number,
-           sizeof(path_id_packet_number));
-  } else {
-    memcpy(nonce + nonce_prefix_size_, &packet_number, sizeof(packet_number));
-  }
+  uint64_t path_id_packet_number =
+      QuicUtils::PackPathIdAndPacketNumber(path_id, packet_number);
+  memcpy(nonce + nonce_prefix_size_, &path_id_packet_number,
+         sizeof(path_id_packet_number));
   if (!EVP_AEAD_CTX_open(
           ctx_.get(), reinterpret_cast<uint8_t*>(output), output_length,
           max_output_length, reinterpret_cast<const uint8_t*>(nonce),