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_server_handshaker.h b/quic/core/quic_crypto_server_handshaker.h
index a1ec99f..544307c 100644
--- a/quic/core/quic_crypto_server_handshaker.h
+++ b/quic/core/quic_crypto_server_handshaker.h
@@ -39,7 +39,7 @@
 
   // From HandshakerDelegate
   void CancelOutstandingCallbacks() override;
-  bool GetBase64SHA256ClientChannelID(QuicString* output) const override;
+  bool GetBase64SHA256ClientChannelID(std::string* output) const override;
   void SendServerConfigUpdate(
       const CachedNetworkParameters* cached_network_params) override;
   uint8_t NumHandshakeMessages() const override;
@@ -139,7 +139,7 @@
   void FinishProcessingHandshakeMessageAfterProcessClientHello(
       const ValidateClientHelloResultCallback::Result& result,
       QuicErrorCode error,
-      const QuicString& error_details,
+      const std::string& error_details,
       std::unique_ptr<CryptoHandshakeMessage> reply,
       std::unique_ptr<DiversificationNonce> diversification_nonce,
       std::unique_ptr<ProofSource::Details> proof_source_details);
@@ -177,7 +177,7 @@
 
   // Hash of the last received CHLO message which can be used for generating
   // server config update messages.
-  QuicString chlo_hash_;
+  std::string chlo_hash_;
 
   // Pointer to the helper for this crypto stream. Must outlive this stream.
   QuicCryptoServerStream::Helper* helper_;