Ad-hoc rate limiting for UDPPort::SendTo failures.

Bug: chromium:856088
Change-Id: I8b9edd8c7392834a7a88987963de2f8e9d37be11
Reviewed-on: https://webrtc-review.googlesource.com/93881
Commit-Queue: Zach Stein <zstein@webrtc.org>
Reviewed-by: Qingsi Wang <qingsi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24411}
diff --git a/p2p/base/stunport.h b/p2p/base/stunport.h
index 9cb479d..76647e8 100644
--- a/p2p/base/stunport.h
+++ b/p2p/base/stunport.h
@@ -242,6 +242,7 @@
   StunRequestManager requests_;
   rtc::AsyncPacketSocket* socket_;
   int error_;
+  int send_error_count_ = 0;
   std::unique_ptr<AddressResolver> resolver_;
   bool ready_;
   int stun_keepalive_delay_;