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_connection.h b/quic/core/quic_connection.h
index 985e44c..43aa1dd 100644
--- a/quic/core/quic_connection.h
+++ b/quic/core/quic_connection.h
@@ -126,7 +126,7 @@
   // Called when the connection is closed either locally by the framer, or
   // remotely by the peer.
   virtual void OnConnectionClosed(QuicErrorCode error,
-                                  const QuicString& error_details,
+                                  const std::string& error_details,
                                   ConnectionCloseSource source) = 0;
 
   // Called when the connection failed to write because the socket was blocked.
@@ -276,7 +276,7 @@
 
   // Called when the connection is closed.
   virtual void OnConnectionClosed(QuicErrorCode error,
-                                  const QuicString& error_details,
+                                  const std::string& error_details,
                                   ConnectionCloseSource source) {}
 
   // Called when the version negotiation is successful.
@@ -407,7 +407,7 @@
   // packet is sent to the peer.
   virtual void CloseConnection(
       QuicErrorCode error,
-      const QuicString& details,
+      const std::string& details,
       ConnectionCloseBehavior connection_close_behavior);
 
   // Returns statistics tracked for this connection.
@@ -519,7 +519,7 @@
 
   // QuicConnectionCloseDelegateInterface
   void OnUnrecoverableError(QuicErrorCode error,
-                            const QuicString& error_details,
+                            const std::string& error_details,
                             ConnectionCloseSource source) override;
 
   // QuicPacketGenerator::DelegateInterface
@@ -917,7 +917,7 @@
   // TODO(fayang): change |ack_mode| to bool |force_sending_ack| when
   // deprecating quic_deprecate_ack_bundling_mode.
   virtual void SendConnectionClosePacket(QuicErrorCode error,
-                                         const QuicString& details,
+                                         const std::string& details,
                                          AckBundling ack_mode);
 
   // Returns true if the packet should be discarded and not sent.
@@ -952,7 +952,7 @@
   // Notifies the visitor of the close and marks the connection as disconnected.
   // Does not send a connection close frame to the peer.
   void TearDownLocalConnectionState(QuicErrorCode error,
-                                    const QuicString& details,
+                                    const std::string& details,
                                     ConnectionCloseSource source);
 
   // Writes the given packet to socket, encrypted with packet's