Avoid cluster set up at max bitrate at start

webrtc/modules/congestion_controller/probe_controller.cc

 /*
  *  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 36 matching lines @@
                                   int max_bitrate_bps) {
   rtc::CritScope cs(&critsect_);
   if (state_ == State::kInit) {
     // When probing at 1.8 Mbps ( 6x 300), this represents a threshold of
     // 1.2 Mbps to continue probing.
     InitiateProbing({3 * start_bitrate_bps, 6 * start_bitrate_bps},
                     4 * start_bitrate_bps);
   }
 
   // Only do probing if:
-  //   - we are mid-call, which we consider to be if
-  //     |estimated_bitrate_bps_| != 0, and
-  //   - the current bitrate is lower than the new |max_bitrate_bps|, and
-  //   - we actually want to increase the |max_bitrate_bps_|.
-  if (estimated_bitrate_bps_ != 0 && estimated_bitrate_bps_ < max_bitrate_bps &&
+  //   we are mid-call, which we consider to be if
+  //     exponential probing is not active and
+  //     |estimated_bitrate_bps_| is valid (> 0) and
+  //     the current bitrate is lower than the new |max_bitrate_bps|, and
+  //     we actually want to increase the |max_bitrate_bps_|.
+  if (state_ != State::kWaitingForProbingResult &&
+      estimated_bitrate_bps_ != 0 &&
+      estimated_bitrate_bps_ < max_bitrate_bps &&
       max_bitrate_bps > max_bitrate_bps_) {
     InitiateProbing({max_bitrate_bps}, kExponentialProbingDisabled);
   }
   max_bitrate_bps_ = max_bitrate_bps;
 }
 
 void ProbeController::SetEstimatedBitrate(int bitrate_bps) {
   rtc::CritScope cs(&critsect_);
   if (state_ == State::kWaitingForProbingResult) {
     if ((clock_->TimeInMilliseconds() - time_last_probing_initiated_ms_) >
@@ skipping 32 matching lines @@
   }
   min_bitrate_to_probe_further_bps_ = min_bitrate_to_probe_further_bps;
   time_last_probing_initiated_ms_ = clock_->TimeInMilliseconds();
   if (min_bitrate_to_probe_further_bps == kExponentialProbingDisabled)
     state_ = State::kProbingComplete;
   else
     state_ = State::kWaitingForProbingResult;
 }
 
 }  // namespace webrtc