Ping backup connection at a slower rate

talk/app/webrtc/peerconnectioninterface.h

Index: talk/app/webrtc/peerconnectioninterface.h
diff --git a/talk/app/webrtc/peerconnectioninterface.h b/talk/app/webrtc/peerconnectioninterface.h
index b7814e583033ac4f741c8d1b245ed14e5c12c143..fdb3349497840229b9c853ebd78f8b489ee1bbcc 100644
--- a/talk/app/webrtc/peerconnectioninterface.h
+++ b/talk/app/webrtc/peerconnectioninterface.h
@@ -253,7 +253,8 @@ class PeerConnectionInterface : public rtc::RefCountInterface {
     TcpCandidatePolicy tcp_candidate_policy;
     int audio_jitter_buffer_max_packets;
     bool audio_jitter_buffer_fast_accelerate;
-    int ice_connection_receiving_timeout;
+    int ice_connection_receiving_timeout;     // ms
+    int ice_backup_connection_ping_interval;  // ms
     ContinualGatheringPolicy continual_gathering_policy;
     std::vector<rtc::scoped_refptr<rtc::RTCCertificate>> certificates;
 
@@ -265,6 +266,7 @@ class PeerConnectionInterface : public rtc::RefCountInterface {
           audio_jitter_buffer_max_packets(kAudioJitterBufferMaxPackets),
           audio_jitter_buffer_fast_accelerate(false),
           ice_connection_receiving_timeout(kUndefined),
+          ice_backup_connection_ping_interval(kUndefined),
           continual_gathering_policy(GATHER_ONCE) {}
   };