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/mock_quic_client_promised_info.cc b/quic/test_tools/mock_quic_client_promised_info.cc
index 4400b03..5b78104 100644
--- a/quic/test_tools/mock_quic_client_promised_info.cc
+++ b/quic/test_tools/mock_quic_client_promised_info.cc
@@ -10,7 +10,7 @@
 MockQuicClientPromisedInfo::MockQuicClientPromisedInfo(
     QuicSpdyClientSessionBase* session,
     QuicStreamId id,
-    QuicString url)
+    std::string url)
     : QuicClientPromisedInfo(session, id, url) {}
 
 MockQuicClientPromisedInfo::~MockQuicClientPromisedInfo() {}