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/crypto/transport_parameters_test.cc b/quic/core/crypto/transport_parameters_test.cc
index 8a81841..23b18e5 100644
--- a/quic/core/crypto/transport_parameters_test.cc
+++ b/quic/core/crypto/transport_parameters_test.cc
@@ -412,7 +412,7 @@
   orig_params.idle_timeout = 56;
 
   orig_params.google_quic_params = QuicMakeUnique<CryptoHandshakeMessage>();
-  const QuicString kTestString = "test string";
+  const std::string kTestString = "test string";
   orig_params.google_quic_params->SetStringPiece(42, kTestString);
   const uint32_t kTestValue = 12;
   orig_params.google_quic_params->SetValue(1337, kTestValue);