Detect situation when there is no missing send completion signal in P2PSocket implementation.

content/common/p2p_socket_type.h

Index: content/common/p2p_socket_type.h
diff --git a/content/common/p2p_socket_type.h b/content/common/p2p_socket_type.h
index b47ae933134ef1c8da8d3b315ccedb569245ff26..ed77296b28de513dc2fcbacb949afd41199342bc 100644
--- a/content/common/p2p_socket_type.h
+++ b/content/common/p2p_socket_type.h
@@ -48,6 +48,16 @@ struct P2PHostAndIPEndPoint {
   net::IPEndPoint ip_address;
 };
 
+// Stuct which keeps track of metrics during a send operation on P2P sockets.
+// Currently, it only carries packet_id but could be expanded to include
+// timestamps when packet arrives at various points.
+struct P2PSendPacketMetrics {
+  P2PSendPacketMetrics() : packet_id(0) {}
+  explicit P2PSendPacketMetrics(uint64_t packet_id) : packet_id(packet_id) {}
+
+  uint64_t packet_id;
+};
+
 }  // namespace content
 
 #endif  // CONTENT_COMMON_P2P_SOCKET_TYPE_H_