In QUIC, use using for alias declaration.

This is the preferred way according to go/cstyle#Aliases

PiperOrigin-RevId: 341926282
Change-Id: Ib70cdb37fbdc985dec9e862c60aacbae54510281
diff --git a/quic/tools/quic_memory_cache_backend.cc b/quic/tools/quic_memory_cache_backend.cc
index f6ecadd..465e0a9 100644
--- a/quic/tools/quic_memory_cache_backend.cc
+++ b/quic/tools/quic_memory_cache_backend.cc
@@ -163,8 +163,8 @@
   return it->second.get();
 }
 
-typedef QuicBackendResponse::ServerPushInfo ServerPushInfo;
-typedef QuicBackendResponse::SpecialResponseType SpecialResponseType;
+using ServerPushInfo = QuicBackendResponse::ServerPushInfo;
+using SpecialResponseType = QuicBackendResponse::SpecialResponseType;
 
 void QuicMemoryCacheBackend::AddSimpleResponse(absl::string_view host,
                                                absl::string_view path,