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/tools/quic_simple_server_stream.h b/quic/tools/quic_simple_server_stream.h
index 2e6826f..4472262 100644
--- a/quic/tools/quic_simple_server_stream.h
+++ b/quic/tools/quic_simple_server_stream.h
@@ -56,7 +56,7 @@
   // Implements QuicSimpleServerBackend::RequestHandler callbacks
   QuicConnectionId connection_id() const override;
   QuicStreamId stream_id() const override;
-  QuicString peer_host() const override;
+  std::string peer_host() const override;
   void OnResponseBackendComplete(
       const QuicBackendResponse* response,
       std::list<QuicBackendResponse::ServerPushInfo> resources) override;
@@ -87,12 +87,12 @@
 
   spdy::SpdyHeaderBlock* request_headers() { return &request_headers_; }
 
-  const QuicString& body() { return body_; }
+  const std::string& body() { return body_; }
 
   // The parsed headers received from the client.
   spdy::SpdyHeaderBlock request_headers_;
   int64_t content_length_;
-  QuicString body_;
+  std::string body_;
 
  private:
   QuicSimpleServerBackend* quic_simple_server_backend_;  // Not owned.