Replace QuicString with std::string, pass 1

This replaces QuicString with std::string in all of the "QUIC proper".  I will
delete QuicString once all code using it is gone.

gfe-relnote: n/a (no functional change)
PiperOrigin-RevId: 237872023
Change-Id: I82de62c9855516b15039734d05155917e68ff4ee
diff --git a/quic/core/quic_buffered_packet_store.cc b/quic/core/quic_buffered_packet_store.cc
index 68ebac9..d5637ca 100644
--- a/quic/core/quic_buffered_packet_store.cc
+++ b/quic/core/quic_buffered_packet_store.cc
@@ -85,7 +85,7 @@
     QuicSocketAddress self_address,
     QuicSocketAddress peer_address,
     bool is_chlo,
-    const QuicString& alpn,
+    const std::string& alpn,
     const ParsedQuicVersion& version) {
   QUIC_BUG_IF(!FLAGS_quic_allow_chlo_buffering)
       << "Shouldn't buffer packets if disabled via flag.";