Probing: Add support for exponential startup probing

webrtc/modules/pacing/bitrate_prober.h

Index: webrtc/modules/pacing/bitrate_prober.h
diff --git a/webrtc/modules/pacing/bitrate_prober.h b/webrtc/modules/pacing/bitrate_prober.h
index cfeb4972f91f3b2c248c6ce9bf14eee0b27b2c33..ae79d48639bb49e5bda9f245863bb86948c10850 100644
--- a/webrtc/modules/pacing/bitrate_prober.h
+++ b/webrtc/modules/pacing/bitrate_prober.h
@@ -31,10 +31,14 @@ class BitrateProber {
   // TimeUntilNextProbe().
   bool IsProbing() const;
 
+  bool IsExpectingProbingResults() const;
+
+  void SetEstimatedBitrate(int bitrate_bps);
+
   // Initializes a new probing session if the prober is allowed to probe. Does
   // not initialize the prober unless the packet size is large enough to probe
   // with.
-  void OnIncomingPacket(size_t packet_size);
+  void OnIncomingPacket(int64_t now_ms, size_t packet_size);
 
   // Create a cluster used to probe for |bitrate_bps| with |num_packets| number
   // of packets.
@@ -51,24 +55,11 @@ class BitrateProber {
   // packet.
   size_t RecommendedPacketSize() const;
 
-  // Called to report to the prober that a packet has been sent, which helps the
-  // prober know when to move to the next packet in a probe.
+  // Notifies the prober that a probe packet has been sent, which helps the
+  // prober move to the next packet in a probe.
   void PacketSent(int64_t now_ms, size_t packet_size);
 
  private:
-  enum class ProbingState {
-    // Probing will not be triggered in this state at all times.
-    kDisabled,
-    // Probing is enabled and ready to trigger on the first packet arrival.
-    kInactive,
-    // Probe cluster is filled with the set of data rates to be probed and
-    // probes are being sent.
-    kActive,
-    // Probing is enabled, but currently suspended until an explicit trigger
-    // to start probing again.
-    kSuspended,
-  };
-
   struct ProbeCluster {
     int max_probe_packets = 0;
     int sent_probe_packets = 0;
@@ -76,10 +67,24 @@ class BitrateProber {
     int id = -1;
   };
 
+  enum class State {
+    // Initial state. No probe clusters have been set up yet for probing.
+    kInit,
+    // Probe clusters have been set up and probes are being sent.
+    kSending,
+    // Probes have been sent, waiting on probing results.
+    kWaitForResult,
+    // Probing is complete. No active probing until an explicit
+    // request for probing.
+    kComplete,
+    // Probing disabled. No probing until explicitly enabled again.
+    kDisabled,
+  };
+
   // Resets the state of the prober and clears any cluster/timing data tracked.
   void ResetState();
 
-  ProbingState probing_state_;
+  State probing_state_;
   // Probe bitrate per packet. These are used to compute the delta relative to
   // the previous probe packet based on the size and time when that packet was
   // sent.
@@ -88,6 +93,8 @@ class BitrateProber {
   // The last time a probe was sent.
   int64_t time_last_probe_sent_ms_;
   int next_cluster_id_;
+  int min_bitrate_to_probe_further_;
+  int estimated_bitrate_bps_;
 };
 }  // namespace webrtc
 #endif  // WEBRTC_MODULES_PACING_BITRATE_PROBER_H_