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_crypto_client_stream_test.cc b/quic/core/quic_crypto_client_stream_test.cc
index d9b344a..bd5162b 100644
--- a/quic/core/quic_crypto_client_stream_test.cc
+++ b/quic/core/quic_crypto_client_stream_test.cc
@@ -188,10 +188,10 @@
   QuicCryptoClientConfig::CachedState* state =
       crypto_config_.LookupOrCreate(server_id_);
 
-  std::vector<QuicString> certs = state->certs();
-  QuicString cert_sct = state->cert_sct();
-  QuicString signature = state->signature();
-  QuicString chlo_hash = state->chlo_hash();
+  std::vector<std::string> certs = state->certs();
+  std::string cert_sct = state->cert_sct();
+  std::string signature = state->signature();
+  std::string chlo_hash = state->chlo_hash();
   state->SetProof(certs, cert_sct, chlo_hash, signature + signature);
 
   EXPECT_CALL(*session_, OnProofVerifyDetailsAvailable(testing::_))
@@ -243,7 +243,7 @@
   // Make sure that the STK and SCFG are cached correctly.
   EXPECT_EQ("xstk", state->source_address_token());
 
-  const QuicString& cached_scfg = state->server_config();
+  const std::string& cached_scfg = state->server_config();
   test::CompareCharArraysWithHexError(
       "scfg", cached_scfg.data(), cached_scfg.length(),
       reinterpret_cast<char*>(scfg), QUIC_ARRAYSIZE(scfg));