Transition ICE gathering state to "new" once all transports go away

Bug: chromium:1115080
Change-Id: I524ed48ffc2520ce21ad4bdc25fa3b86d9e41af5
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/182081
Reviewed-by: Guido Urdaneta <guidou@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31976}
diff --git a/pc/peer_connection.cc b/pc/peer_connection.cc
index 7cee2c7..6a5ad95 100644
--- a/pc/peer_connection.cc
+++ b/pc/peer_connection.cc
@@ -7024,6 +7024,11 @@
     OnIceGatheringChange(PeerConnectionInterface::kIceGatheringGathering);
   } else if (state == cricket::kIceGatheringComplete) {
     OnIceGatheringChange(PeerConnectionInterface::kIceGatheringComplete);
+  } else if (state == cricket::kIceGatheringNew) {
+    OnIceGatheringChange(PeerConnectionInterface::kIceGatheringNew);
+  } else {
+    RTC_LOG(LS_ERROR) << "Unknown state received: " << state;
+    RTC_NOTREACHED();
   }
 }