Notify NQE of TCP RTT values

net/base/socket_performance_watcher.h

 // Copyright 2015 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_BASE_SOCKET_PERFORMANCE_WATCHER_H_
 #define NET_BASE_SOCKET_PERFORMANCE_WATCHER_H_
 
 #include "base/macros.h"
+#include "base/time/time.h"
 #include "net/base/net_export.h"
 #include "net/base/socket_performance_watcher_factory.h"
 
 namespace base {
 class TimeDelta;
 }  // namespace base
 
 namespace net {
 
 // SocketPerformanceWatcher is the base class for recording and aggregating
 // socket statistics.
 class NET_EXPORT_PRIVATE SocketPerformanceWatcher {
  public:
   // |socket_performance_watcher_factory| is the factory that constructed
   // |this| watcher.
   SocketPerformanceWatcher(
       const SocketPerformanceWatcherFactory::Protocol protocol,
       SocketPerformanceWatcherFactory* socket_performance_watcher_factory);
 
   virtual ~SocketPerformanceWatcher();
 
   // Called when updated transport layer RTT information is available. This
   // must be the transport layer RTT from this device to the remote transport
   // layer endpoint. This method is called immediately after the observation is
   // made, hence no timestamp.
   void OnUpdatedRTTAvailable(const base::TimeDelta& rtt) const;
 
+  base::TimeDelta rtt_notification_interval() const {
+    // TODO(tbansal): TCP/QUIC start with a hard-coded RTT estimate, and
+    // converge to a more accurate value as more packets are received. This
+    // function should be changed to return 0 seconds until this connection
+    // has received 15 packets. Afterwards, it should return 2 seconds.

[Ryan Sleevi, 2016/02/25 22:48:46]

Why not return this as a "const base::TimeDelta&" ?

Also, this comment seems like it belongs in a crbug.com, not here.

[tbansal1, 2016/02/26 23:43:34]

I think mmenke said at one point that it is okay to return TimeDelta by value,
because that class only contains an int64 member. I can't find that comment in
the review history, so I may be wrong. Also, codesearch shows it not returned by
reference 2200 times
(https://code.google.com/p/chromium/codesearch#search/&q=TimeDelta%5C%20%5BA-Z...),
and by reference 500 times
(https://code.google.com/p/chromium/codesearch#search/&q=TimeDelta&%5C%20%...).
I was going to fix that in the next CL but filed a new bug (crbug.com/590300).

+    return rtt_notification_interval_;
+  }
+
+  // Called when |this| socket performance watcher is reused for establishing a
+  // new transport layer connection.
+  void Reset() const;
+
  private:
   // Transport layer protocol used by the socket that |this| is watching.
   const SocketPerformanceWatcherFactory::Protocol protocol_;
 
+  // Minimum time interval between two successive OnUpdatedRTTAvailable
+  // notifications to |this|.
+  const base::TimeDelta rtt_notification_interval_;
+
   // |socket_performance_watcher_factory_| is the factory that created
   // |this| watcher.
   SocketPerformanceWatcherFactory* socket_performance_watcher_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SocketPerformanceWatcher);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_SOCKET_PERFORMANCE_WATCHER_H_