Fix all Performance and Bug-Prone patterns in quic/core. No functional change. Not flag protected.

net/tools/quic/quic_per_connection_packet_writer.h

Index: net/tools/quic/quic_per_connection_packet_writer.h
diff --git a/net/tools/quic/quic_per_connection_packet_writer.h b/net/tools/quic/quic_per_connection_packet_writer.h
index 08e5e01bdacdc77dee59902053fdbf8224bbc46d..cc48b635e1476bf3a898c12fd7c7717b1512cdc7 100644
--- a/net/tools/quic/quic_per_connection_packet_writer.h
+++ b/net/tools/quic/quic_per_connection_packet_writer.h
@@ -17,7 +17,7 @@ namespace net {
 class QuicPerConnectionPacketWriter : public QuicPacketWriter {
  public:
   // Does not take ownership of |shared_writer|.
-  QuicPerConnectionPacketWriter(QuicPacketWriter* shared_writer);
+  explicit QuicPerConnectionPacketWriter(QuicPacketWriter* shared_writer);
   ~QuicPerConnectionPacketWriter() override;
 
   QuicPacketWriter* shared_writer() const { return shared_writer_; }