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/test_tools/simulator/port.h b/quic/test_tools/simulator/port.h
index 5cd4a7f..15da638 100644
--- a/quic/test_tools/simulator/port.h
+++ b/quic/test_tools/simulator/port.h
@@ -19,11 +19,11 @@
   ~Packet();
   Packet(const Packet& packet);
 
-  QuicString source;
-  QuicString destination;
+  std::string source;
+  std::string destination;
   QuicTime tx_timestamp;
 
-  QuicString contents;
+  std::string contents;
   QuicByteCount size;
 };
 
@@ -57,7 +57,7 @@
   virtual void SetTxPort(ConstrainedPortInterface* port) = 0;
 
  protected:
-  Endpoint(Simulator* simulator, QuicString name);
+  Endpoint(Simulator* simulator, std::string name);
 };
 
 }  // namespace simulator