Change quicpacketwriter::getnextwritelocation to return a release function used to free a writer-allocated buffer. use this release function to avoid buffer leak if a writer buffer is allocated but writer->writepacket is not called. protected by --gfe2_reloadable_flag_quic_avoid_leak_writer_buffer.

This is needed to fix a buffer leak when the new PigeonWriter is used.

PiperOrigin-RevId: 312369772
Change-Id: I0d12327b58989ec69e401b03f7b9ebb4d8ce22fd
diff --git a/quic/core/quic_connection.h b/quic/core/quic_connection.h
index 3f4329c..87c049b 100644
--- a/quic/core/quic_connection.h
+++ b/quic/core/quic_connection.h
@@ -596,7 +596,7 @@
   bool ShouldGeneratePacket(HasRetransmittableData retransmittable,
                             IsHandshake handshake) override;
   const QuicFrames MaybeBundleAckOpportunistically() override;
-  char* GetPacketBuffer() override;
+  QuicPacketBuffer GetPacketBuffer() override;
   void OnSerializedPacket(SerializedPacket packet) override;
   void OnUnrecoverableError(QuicErrorCode error,
                             const std::string& error_details) override;