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/tools/quic_simple_crypto_server_stream_helper.cc b/quic/tools/quic_simple_crypto_server_stream_helper.cc
index bdd6731..2bb9656 100644
--- a/quic/tools/quic_simple_crypto_server_stream_helper.cc
+++ b/quic/tools/quic_simple_crypto_server_stream_helper.cc
@@ -27,7 +27,7 @@
     const QuicSocketAddress& client_address,
     const QuicSocketAddress& peer_address,
     const QuicSocketAddress& self_address,
-    QuicString* error_details) const {
+    std::string* error_details) const {
   return true;
 }