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/quic_decrypter.h b/quic/core/crypto/quic_decrypter.h
index c7c2ccc..f55b00b 100644
--- a/quic/core/crypto/quic_decrypter.h
+++ b/quic/core/crypto/quic_decrypter.h
@@ -73,8 +73,8 @@
                                       const DiversificationNonce& nonce,
                                       size_t key_size,
                                       size_t nonce_prefix_size,
-                                      QuicString* out_key,
-                                      QuicString* out_nonce_prefix);
+                                      std::string* out_key,
+                                      std::string* out_nonce_prefix);
 };
 
 }  // namespace quic