Now probe for x3 and x6 the initial start bitrate.

webrtc/modules/congestion_controller/probe_bitrate_estimator_unittest.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 42 matching lines @@
   AddPacketFeedback(0, 1000, 0, 15);
   AddPacketFeedback(0, 1000, 10, 30);
   AddPacketFeedback(0, 1000, 20, 35);
   AddPacketFeedback(0, 1000, 30, 40);
 
   EXPECT_NEAR(measured_bps_, 800000, 10);
 }
 
 TEST_F(TestProbeBitrateEstimator, TooFastReceive) {
   AddPacketFeedback(0, 1000, 0, 19);
-  AddPacketFeedback(0, 1000, 10, 30);
-  AddPacketFeedback(0, 1000, 20, 40);
-  AddPacketFeedback(0, 1000, 40, 50);
+  AddPacketFeedback(0, 1000, 10, 22);
+  AddPacketFeedback(0, 1000, 20, 25);
+  AddPacketFeedback(0, 1000, 40, 27);
 
   EXPECT_EQ(measured_bps_, INVALID_BPS);
 }
 
 TEST_F(TestProbeBitrateEstimator, SlowReceive) {
   AddPacketFeedback(0, 1000, 0, 10);
   AddPacketFeedback(0, 1000, 10, 40);
   AddPacketFeedback(0, 1000, 20, 70);
   AddPacketFeedback(0, 1000, 30, 85);
 
@@ skipping 60 matching lines @@
 TEST_F(TestProbeBitrateEstimator, IgnoreSizeFirstReceivePacket) {
   AddPacketFeedback(0, 1500, 0, 10);
   AddPacketFeedback(0, 1000, 10, 20);
   AddPacketFeedback(0, 1000, 20, 30);
   AddPacketFeedback(0, 1000, 30, 40);
 
   EXPECT_NEAR(measured_bps_, 800000, 10);
 }
 
 }  // namespace webrtc