Wire up packet_id / send time callbacks to webrtc via libjingle.

BUG=webrtc:4173

Review URL: https://codereview.webrtc.org/1363573002

Cr-Commit-Position: refs/heads/master@{#10289}
diff --git a/webrtc/base/socket.h b/webrtc/base/socket.h
index 8d98d27..22326cb 100644
--- a/webrtc/base/socket.h
+++ b/webrtc/base/socket.h
@@ -124,6 +124,15 @@
   return (e == EWOULDBLOCK) || (e == EAGAIN) || (e == EINPROGRESS);
 }
 
+struct SentPacket {
+  SentPacket() : packet_id(-1), send_time_ms(-1) {}
+  SentPacket(int packet_id, int64_t send_time_ms)
+      : packet_id(packet_id), send_time_ms(send_time_ms) {}
+
+  int packet_id;
+  int64_t send_time_ms;
+};
+
 // General interface for the socket implementations of various networks.  The
 // methods match those of normal UNIX sockets very closely.
 class Socket {