Implement periodic bandwidth probing in application-limited region.

webrtc/modules/pacing/alr_detector.h

 /*
  *  Copyright (c) 2016 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.
  */
 
@@ skipping 17 matching lines @@
 class AlrDetector {
  public:
   AlrDetector();
   ~AlrDetector();
 
   void OnBytesSent(size_t bytes_sent, int64_t now_ms);
 
   // Set current estimated bandwidth.
   void SetEstimatedBitrate(int bitrate_bps);
 
-  // Returns true if currently in application-limited region.
-  bool InApplicationLimitedRegion() const;
+  // Returns time in milliseconds when the current application-limited region
+  // started or empty result if the sender is currently not application-limited.
+  rtc::Optional<int64_t> GetApplicationLimitedRegionStartTime() const;
 
  private:
   RateStatistics rate_;
   int estimated_bitrate_bps_ = 0;
-  bool application_limited_ = false;
+
+  // Non-empty in ALR state.
+  rtc::Optional<int64_t> alr_started_time_ms_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_PACING_ALR_DETECTOR_H_