Completed the functionalities of SrtpTransport.

webrtc/p2p/base/fakepackettransport.h

Index: webrtc/p2p/base/fakepackettransport.h
diff --git a/webrtc/p2p/base/fakepackettransport.h b/webrtc/p2p/base/fakepackettransport.h
index 16af9a42aec5a5241e38b223cbd8dba7982e277a..bee4d19e59d6b2fdb7766105ec6e246be210c884 100644
--- a/webrtc/p2p/base/fakepackettransport.h
+++ b/webrtc/p2p/base/fakepackettransport.h
@@ -86,6 +86,14 @@ class FakePacketTransport : public PacketTransportInternal {
   bool GetOption(Socket::Option opt, int* value) override { return true; }
   int GetError() override { return 0; }
 
+  void set_last_received_packet(rtc::CopyOnWriteBuffer* packet) {
+    last_received_packet_ = *packet;
+  }

[Taylor Brandstetter, 2017/08/23 22:13:29]

Can this be private and called internally? Instead of SendPacketInternal calling
SignalReadPacket, it could call a private "HandleReceivedPacket" method which
both sets last_received_packet_ and calls SignalReadPacket.

[Zhi Huang, 2017/08/24 23:38:07]

We can just store the last sent packet before trigger the signal and have a
getter for it.

+
+  const CopyOnWriteBuffer* last_received_packet() {
+    return &last_received_packet_;
+  }
+
  private:
   void set_writable(bool writable) {
     if (writable_ == writable) {
@@ -113,6 +121,7 @@ class FakePacketTransport : public PacketTransportInternal {
     }
   }
 
+  CopyOnWriteBuffer last_received_packet_;
   AsyncInvoker invoker_;
   std::string debug_name_;
   FakePacketTransport* dest_ = nullptr;