Add a histogram metric tracking for how long audio RTP packets are sent

webrtc/audio/time_interval.h

+/*
+ *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_AUDIO_TIME_INTERVAL_H_
+#define WEBRTC_AUDIO_TIME_INTERVAL_H_
+
+#include <stdint.h>
+
+#include "webrtc/rtc_base/optional.h"
+
+namespace webrtc {
+
+// This class logs the first and last time its Extend() function is called.
+//
+// This class is not thread-safe; Extend() calls should only be made by a
+// single thread at a time, such as within a lock or destructor.
+//
+// Example usage:
+//   // let x < y < z < u < v
+//   rtc::TimeInterval interval;
+//   ...  //   interval.Extend(); // at time x
+//   ...
+//   interval.Extend(); // at time y
+//   ...
+//   interval.Extend(); // at time u
+//   ...
+//   interval.Extend(z); // at time v
+//   ...
+//   if (!interval.Empty()) {
+//     int64_t active_time = interval.Length(); // returns (u - x)
+//   }
+class TimeInterval {
+ public:
+  TimeInterval();
+  ~TimeInterval();
+  // Extend the interval with the current time.
+  void Extend();
+  // Extend the interval with a given time.
+  void Extend(int64_t time);
+  // Take the convex hull with another interval.

[saza WebRTC, 2017/07/18 09:39:28]

Original line:
// Extend the interval with another interval.
ossu@'s comment:
It may be prudent to note here that this interval is extended with the times
(first and last) of other_interval and not with the length of the other
interval. (So extending an interval with itself will not double the length).
Though maybe that's obvious?

+  void Extend(const TimeInterval& other_interval);
+  // True iff Extend has never been called.
+  bool Empty() const;
+  // Returns the time between the first and the last tick, in milliseconds.
+  int64_t Length() const;
+
+ private:
+  struct Interval {
+    Interval(int64_t first, int64_t last);
+
+    int64_t first, last;
+  };
+  rtc::Optional<Interval> interval_;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_AUDIO_TIME_INTERVAL_H_