Probing: Add support for exponential startup probing

webrtc/modules/pacing/paced_sender.h

Index: webrtc/modules/pacing/paced_sender.h
diff --git a/webrtc/modules/pacing/paced_sender.h b/webrtc/modules/pacing/paced_sender.h
index b0d7076875238eca24d04e20e2f3d6a19d9a0607..3990da671bf488f9c148fc3d6d38911d373a2b83 100644
--- a/webrtc/modules/pacing/paced_sender.h
+++ b/webrtc/modules/pacing/paced_sender.h
@@ -15,6 +15,7 @@
 #include <memory>
 #include <set>
 
+#include "webrtc/base/checks.h"
 #include "webrtc/base/thread_annotations.h"
 #include "webrtc/modules/include/module.h"
 #include "webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h"
@@ -130,6 +131,8 @@ class PacedSender : public Module, public RtpPacketSender {
   // Process any pending packets in the queue(s).
   void Process() override;
 
+  bool IsExpectingProbingResults() const;
+
  private:
   // Updates the number of bytes that can be sent for the next time interval.
   void UpdateBytesPerInterval(int64_t delta_time_in_ms)