When all connections timed out on writing, delete them all.

webrtc/p2p/base/p2ptransportchannel.h

Index: webrtc/p2p/base/p2ptransportchannel.h
diff --git a/webrtc/p2p/base/p2ptransportchannel.h b/webrtc/p2p/base/p2ptransportchannel.h
index e49fc2732381abdfd7e9d51f391633157d62f93d..9efb96c42d091759b28d5c25b21a96ab52228359 100644
--- a/webrtc/p2p/base/p2ptransportchannel.h
+++ b/webrtc/p2p/base/p2ptransportchannel.h
@@ -158,6 +158,9 @@ class P2PTransportChannel : public TransportChannelImpl,
   // Public for unit tests.
   Connection* FindNextPingableConnection();
 
+  // Public for unit tests.
+  const std::vector<Connection*>& connections() const { return connections_; }
+
  private:
   rtc::Thread* thread() { return worker_thread_; }
   PortAllocatorSession* allocator_session() {