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_handshake_message.cc b/quic/core/crypto/crypto_handshake_message.cc
index a057254..46577b3 100644
--- a/quic/core/crypto/crypto_handshake_message.cc
+++ b/quic/core/crypto/crypto_handshake_message.cc
@@ -85,7 +85,7 @@
 
 void CryptoHandshakeMessage::SetStringPiece(QuicTag tag,
                                             QuicStringPiece value) {
-  tag_value_map_[tag] = QuicString(value);
+  tag_value_map_[tag] = std::string(value);
 }
 
 void CryptoHandshakeMessage::Erase(QuicTag tag) {
@@ -236,7 +236,7 @@
   return minimum_size_;
 }
 
-QuicString CryptoHandshakeMessage::DebugString() const {
+std::string CryptoHandshakeMessage::DebugString() const {
   return DebugStringInternal(0);
 }
 
@@ -261,11 +261,12 @@
   return ret;
 }
 
-QuicString CryptoHandshakeMessage::DebugStringInternal(size_t indent) const {
-  QuicString ret = QuicString(2 * indent, ' ') + QuicTagToString(tag_) + "<\n";
+std::string CryptoHandshakeMessage::DebugStringInternal(size_t indent) const {
+  std::string ret =
+      std::string(2 * indent, ' ') + QuicTagToString(tag_) + "<\n";
   ++indent;
   for (auto it = tag_value_map_.begin(); it != tag_value_map_.end(); ++it) {
-    ret += QuicString(2 * indent, ' ') + QuicTagToString(it->first) + ": ";
+    ret += std::string(2 * indent, ' ') + QuicTagToString(it->first) + ": ";
 
     bool done = false;
     switch (it->first) {
@@ -371,7 +372,7 @@
     ret += "\n";
   }
   --indent;
-  ret += QuicString(2 * indent, ' ') + ">";
+  ret += std::string(2 * indent, ' ') + ">";
   return ret;
 }