Add flakiness check if there is no received packets in a certain period.

webrtc/p2p/base/fakesession.h

Index: webrtc/p2p/base/fakesession.h
diff --git a/webrtc/p2p/base/fakesession.h b/webrtc/p2p/base/fakesession.h
index a197885ecdc7a9fa2af078331d47e4344ab2d518..c6da75480f671eab977917795e505b300fac24e9 100644
--- a/webrtc/p2p/base/fakesession.h
+++ b/webrtc/p2p/base/fakesession.h
@@ -177,6 +177,10 @@ class FakeTransportChannel : public TransportChannelImpl,
       SignalConnectionRemoved(this);
   }
 
+  void SetReceiving(bool receiving) {
+    set_receiving(receiving);
+  }
+
   virtual int SendPacket(const char* data, size_t len,
                          const rtc::PacketOptions& options, int flags) {
     if (state_ != STATE_CONNECTED) {