Fixed typos and includes in the Quartc API.

This change ensures every .h file is including the headers it's actually
using, and fixes some typos in comments.

BUG=None.

Review-Url: https://codereview.chromium.org/2467093003
Cr-Commit-Position: refs/heads/master@{#429382}
diff --git a/net/quic/quartc/quartc_session_interface.h b/net/quic/quartc/quartc_session_interface.h
index 0957805f..f1513ce 100644
--- a/net/quic/quartc/quartc_session_interface.h
+++ b/net/quic/quartc/quartc_session_interface.h
@@ -7,7 +7,9 @@
 
 #include <stddef.h>
 #include <stdint.h>
+#include <string>
 
+#include "net/base/net_export.h"
 #include "net/quic/quartc/quartc_stream_interface.h"
 
 namespace net {