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_control_frame_manager.h b/quic/core/quic_control_frame_manager.h
index 618f3f9..355179a 100644
--- a/quic/core/quic_control_frame_manager.h
+++ b/quic/core/quic_control_frame_manager.h
@@ -43,7 +43,7 @@
   // immediately.
   void WriteOrBufferGoAway(QuicErrorCode error,
                            QuicStreamId last_good_stream_id,
-                           const QuicString& reason);
+                           const std::string& reason);
 
   // Tries to send a WINDOW_UPDATE_FRAME. Buffers the frame if it cannot be sent
   // immediately.