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/crypto_framer.cc b/quic/core/crypto/crypto_framer.cc
index dfd9eab..d8a32bc 100644
--- a/quic/core/crypto/crypto_framer.cc
+++ b/quic/core/crypto/crypto_framer.cc
@@ -75,7 +75,7 @@
   return error_;
 }
 
-const QuicString& CryptoFramer::error_detail() const {
+const std::string& CryptoFramer::error_detail() const {
   return error_detail_;
 }
 
@@ -329,7 +329,7 @@
       break;
   }
   // Save any remaining data.
-  buffer_ = QuicString(reader.PeekRemainingPayload());
+  buffer_ = std::string(reader.PeekRemainingPayload());
   return QUIC_NO_ERROR;
 }