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/packet_number_indexed_queue_test.cc b/quic/core/packet_number_indexed_queue_test.cc
index 294d2a4..7643fe4 100644
--- a/quic/core/packet_number_indexed_queue_test.cc
+++ b/quic/core/packet_number_indexed_queue_test.cc
@@ -18,7 +18,7 @@
   PacketNumberIndexedQueueTest() {}
 
  protected:
-  PacketNumberIndexedQueue<QuicString> queue_;
+  PacketNumberIndexedQueue<std::string> queue_;
 };
 
 TEST_F(PacketNumberIndexedQueueTest, InitialState) {