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/http/quic_server_session_base.h b/quic/core/http/quic_server_session_base.h
index 55a8d60..7332640 100644
--- a/quic/core/http/quic_server_session_base.h
+++ b/quic/core/http/quic_server_session_base.h
@@ -47,7 +47,7 @@
 
   // Override the base class to cancel any ongoing asychronous crypto.
   void OnConnectionClosed(QuicErrorCode error,
-                          const QuicString& error_details,
+                          const std::string& error_details,
                           ConnectionCloseSource source) override;
 
   // Sends a server config update to the client, containing new bandwidth
@@ -66,7 +66,7 @@
   // client.
   void OnConfigNegotiated() override;
 
-  void set_serving_region(const QuicString& serving_region) {
+  void set_serving_region(const std::string& serving_region) {
     serving_region_ = serving_region;
   }
 
@@ -120,7 +120,7 @@
 
   // Text describing server location. Sent to the client as part of the bandwith
   // estimate in the source-address token. Optional, can be left empty.
-  QuicString serving_region_;
+  std::string serving_region_;
 
   // Time at which we send the last SCUP to the client.
   QuicTime last_scup_time_;