Add UMA for the kernel's TCP RTT estimate.

net/socket/tcp_client_socket.h

Index: net/socket/tcp_client_socket.h
diff --git a/net/socket/tcp_client_socket.h b/net/socket/tcp_client_socket.h
index 0b8062bfd093d02d92253faa4ace3825bf09a067..064b5eb53ee5057cb016d6180bee8838e8f474d2 100644
--- a/net/socket/tcp_client_socket.h
+++ b/net/socket/tcp_client_socket.h
@@ -96,6 +96,10 @@ class NET_EXPORT TCPClientSocket : public StreamSocket {
 
   int OpenSocket(AddressFamily family);
 
+  // Emits histograms for TCP metrics, at the time the socket is
+  // disconnected.
+  void EmitTCPMetricsHistogramsOnDisconnect();
+
   scoped_ptr<TCPSocket> socket_;
 
   // Local IP address and port we are bound to. Set to NULL if Bind()