Fix per regression in probing.

BUG=chromium:687030

Review-Url: https://codereview.webrtc.org/2664193002
Cr-Commit-Position: refs/heads/master@{#16381}

webrtc/modules/pacing/bitrate_prober.cc

diff --git a/webrtc/modules/pacing/bitrate_prober.cc b/webrtc/modules/pacing/bitrate_prober.cc
index 37bdecf..749aa69 100644
--- a/webrtc/modules/pacing/bitrate_prober.cc
+++ b/webrtc/modules/pacing/bitrate_prober.cc
@@ -141,7 +141,7 @@
 // feasible.
 size_t BitrateProber::RecommendedMinProbeSize() const {
   RTC_DCHECK(!clusters_.empty());
-  return clusters_.front().bitrate_bps * 3 * kMinProbeDeltaMs / (8 * 1000);
+  return clusters_.front().bitrate_bps * 2 * kMinProbeDeltaMs / (8 * 1000);
 }
 
 void BitrateProber::ProbeSent(int64_t now_ms, size_t bytes) {