Probing: Add support for exponential startup probing

webrtc/modules/pacing/bitrate_prober.cc

 /*
  *  Copyright (c) 2014 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 48 matching lines @@
   // Don't initialize probing unless we have something large enough to start
   // probing.
   if (probing_state_ == ProbingState::kInactive &&
       !clusters_.empty() &&
       packet_size >= PacedSender::kMinProbePacketSize) {
     probing_state_ = ProbingState::kActive;
   }
 }
 
 void BitrateProber::CreateProbeCluster(int bitrate_bps, int num_packets) {
+  RTC_DCHECK(probing_state_ != ProbingState::kDisabled);
   ProbeCluster cluster;
   cluster.max_probe_packets = num_packets;
   cluster.probe_bitrate_bps = bitrate_bps;
   cluster.id = next_cluster_id_++;
   clusters_.push(cluster);
   LOG(LS_INFO) << "Probe cluster (bitrate:packets): ("
                << cluster.probe_bitrate_bps << ":" << cluster.max_probe_packets
                << ") ";
   if (probing_state_ != ProbingState::kActive)
     probing_state_ = ProbingState::kInactive;
@@ skipping 77 matching lines @@
   if (!clusters_.empty()) {
     ProbeCluster* cluster = &clusters_.front();
     ++cluster->sent_probe_packets;
     if (cluster->sent_probe_packets == cluster->max_probe_packets)
       clusters_.pop();
     if (clusters_.empty())
       probing_state_ = ProbingState::kSuspended;
   }
 }
 }  // namespace webrtc