Ping backup connection at a slower rate

webrtc/p2p/base/transport.h

Index: webrtc/p2p/base/transport.h
diff --git a/webrtc/p2p/base/transport.h b/webrtc/p2p/base/transport.h
index 2e3981243e8e064d825a7df7288bfc8361e9879e..6b4b37d4c56b89e0abc9617ff58b1fc92d96170e 100644
--- a/webrtc/p2p/base/transport.h
+++ b/webrtc/p2p/base/transport.h
@@ -140,7 +140,11 @@ struct TransportStats {
 // Information about ICE configuration.
 struct IceConfig {
   // The ICE connection receiving timeout value.
+  // TODO(honghaiz): Remove suffix _ms to be consistent.
   int receiving_timeout_ms = -1;
+  // Time interval in milliseconds to ping a backup connection when the ICE
+  // channel is strongly connected.
+  int backup_connection_ping_interval = -1;
   // If true, the most recent port allocator session will keep on running.
   bool gather_continually = false;
 };