Cease all future TURN requests when a TURN refresh request fails for a given TURN port.
This fixes an assert error in Turnport::OnSendStunPacket

BUG=webrtc:5388

Review URL: https://codereview.webrtc.org/1547373002

Cr-Commit-Position: refs/heads/master@{#11152}
diff --git a/webrtc/p2p/base/stunrequest.cc b/webrtc/p2p/base/stunrequest.cc
index 0a0b1a8..ce0364e 100644
--- a/webrtc/p2p/base/stunrequest.cc
+++ b/webrtc/p2p/base/stunrequest.cc
@@ -53,11 +53,13 @@
   }
 }
 
-void StunRequestManager::Flush() {
+void StunRequestManager::Flush(int msg_type) {
   for (const auto kv : requests_) {
     StunRequest* request = kv.second;
-    thread_->Clear(request, MSG_STUN_SEND);
-    thread_->Send(request, MSG_STUN_SEND, NULL);
+    if (msg_type == kAllRequests || msg_type == request->type()) {
+      thread_->Clear(request, MSG_STUN_SEND);
+      thread_->Send(request, MSG_STUN_SEND, NULL);
+    }
   }
 }