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_server_id_test.cc b/quic/core/quic_server_id_test.cc
index e7a2abe..01e5a81 100644
--- a/quic/core/quic_server_id_test.cc
+++ b/quic/core/quic_server_id_test.cc
@@ -116,7 +116,7 @@
 }
 
 TEST_F(QuicServerIdTest, EstimateMemoryUsage) {
-  QuicString host = "this is a rather very quite long hostname";
+  std::string host = "this is a rather very quite long hostname";
   uint16_t port = 10;
   bool privacy_mode_enabled = true;
   QuicServerId server_id(host, port, privacy_mode_enabled);