Convert CryptoFramer::ConstructHandshakeMessage to return unique_ptr

gfe-relnote: Use unique_ptr for memory management rather than bare pointer. No functional change intended, not flag-protected.
PiperOrigin-RevId: 238454581
Change-Id: I2f0875854d8bc1983c2e5197abab7741d1985028
diff --git a/quic/core/crypto/crypto_handshake_message.cc b/quic/core/crypto/crypto_handshake_message.cc
index d31a568..1bbed74 100644
--- a/quic/core/crypto/crypto_handshake_message.cc
+++ b/quic/core/crypto/crypto_handshake_message.cc
@@ -58,7 +58,7 @@
 
 const QuicData& CryptoHandshakeMessage::GetSerialized() const {
   if (!serialized_.get()) {
-    serialized_.reset(CryptoFramer::ConstructHandshakeMessage(*this));
+    serialized_ = CryptoFramer::ConstructHandshakeMessage(*this);
   }
   return *serialized_;
 }