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/simulator.h b/quic/test_tools/simulator/simulator.h
index 0180dcb..e21dd50 100644
--- a/quic/test_tools/simulator/simulator.h
+++ b/quic/test_tools/simulator/simulator.h
@@ -130,7 +130,7 @@
   // For each actor, maintain the time it is scheduled at.  The value for
   // unscheduled actors is QuicTime::Infinite().
   QuicUnorderedMap<Actor*, QuicTime> scheduled_times_;
-  QuicUnorderedSet<QuicString> actor_names_;
+  QuicUnorderedSet<std::string> actor_names_;
 };
 
 template <class TerminationPredicate>