Add a PacketOptions struct to webrtc::Transport.

webrtc/transport.h

Index: webrtc/transport.h
diff --git a/webrtc/transport.h b/webrtc/transport.h
index 86b3e2e5ea8169c0f97c312fd84a765a37d6af5e..7b62f6543dcb399ae6d060eb5356a72d64d4a2a3 100644
--- a/webrtc/transport.h
+++ b/webrtc/transport.h
@@ -17,9 +17,17 @@
 
 namespace webrtc {
 
+struct PacketOptions {
+  // A 16 bits positive id. Negative ids are invalid and should be interpreted
+  // as packet_id not being set.
+  int packet_id = -1;
+};
+
 class Transport {
  public:
-  virtual bool SendRtp(const uint8_t* packet, size_t length) = 0;
+  virtual bool SendRtp(const uint8_t* packet,
+                       size_t length,
+                       const PacketOptions& options) = 0;
   virtual bool SendRtcp(const uint8_t* packet, size_t length) = 0;
 
  protected: