Clean up type usage and fix MSVC "truncated value" warnings in net/quic/.

net/quic/quic_sent_packet_manager.cc

Index: net/quic/quic_sent_packet_manager.cc
diff --git a/net/quic/quic_sent_packet_manager.cc b/net/quic/quic_sent_packet_manager.cc
index ebb78f1d4fef88264a812ae4f42f85d3487bc06f..56c327cb6150e9bd56385cece38a307fc2183dab 100644
--- a/net/quic/quic_sent_packet_manager.cc
+++ b/net/quic/quic_sent_packet_manager.cc
@@ -285,7 +285,7 @@ void QuicSentPacketManager::HandleAckForSentPackets(
       // threshold is to tolerate re-ordering.  This handles both StretchAcks
       // and Forward Acks.
       // The nack count only increases when the largest observed increases.
-      size_t min_nacks = ack_frame.largest_observed - sequence_number;
+      QuicPacketCount min_nacks = ack_frame.largest_observed - sequence_number;
       // Truncated acks can nack the largest observed, so use a min of 1.
       if (min_nacks == 0) {
         min_nacks = 1;