Add UMA for the kernel's TCP RTT estimate.

net/socket/tcp_socket_win.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_SOCKET_TCP_SOCKET_WIN_H_
 #define NET_SOCKET_TCP_SOCKET_WIN_H_
 
 #include <winsock2.h>
 
 #include "base/basictypes.h"
@@ skipping 55 matching lines @@
   // - Increase the socket buffer sizes for WinXP;
   // - SetNoDelay(true);
   // - SetKeepAlive(true, 45).
   void SetDefaultOptionsForClient();
   int SetExclusiveAddrUse();
   int SetReceiveBufferSize(int32 size);
   int SetSendBufferSize(int32 size);
   bool SetKeepAlive(bool enable, int delay);
   bool SetNoDelay(bool no_delay);
 
+  // Gets the estimated RTT. Returns false if the RTT is
+  // unavailable. May also return false when estimated RTT is 0.
+  bool GetEstimatedRoundTripTime(base::TimeDelta* out_rtt) const
+      WARN_UNUSED_RESULT;
+
   void Close();
 
   // Setter/Getter methods for TCP FastOpen socket option.
   // NOOPs since TCP FastOpen is not implemented in Windows.
   bool UsingTCPFastOpen() const { return false; }
   void EnableTCPFastOpenIfSupported() {}
 
   bool IsValid() const { return socket_ != INVALID_SOCKET; }
 
   // Marks the start/end of a series of connect attempts for logging purpose.
@@ skipping 63 matching lines @@
   bool logging_multiple_connect_attempts_;
 
   BoundNetLog net_log_;
 
   DISALLOW_COPY_AND_ASSIGN(TCPSocketWin);
 };
 
 }  // namespace net
 
 #endif  // NET_SOCKET_TCP_SOCKET_WIN_H_