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 c2f9ad8c4713db52ea8d000b6ca1d554d31d5adf..ef1d179ff216fb007e5bede5f6f178ccf902f1a7 100644
--- a/webrtc/modules/pacing/bitrate_prober.h
+++ b/webrtc/modules/pacing/bitrate_prober.h
@@ -25,6 +25,19 @@ class BitrateProber {
  public:
   BitrateProber();
 
+  enum class State {
+    // Probing will not be triggered in this state at all times.
+    kDisabled,
+    // Probing is enabled, but currently inactive.
+    kInactive,
+    // Probe cluster is filled with the set of data rates to be probed and
+    // probing is active.
+    kActive,
+    // Probing is enabled and complete. No active probing until an explicit
+    // request comes in again.
+    kComplete,
+  };
+
   void SetEnabled(bool enable);
 
   // Returns true if the prober is in a probing session, i.e., it currently
@@ -32,12 +45,11 @@ class BitrateProber {
   // TimeUntilNextProbe().
   bool IsProbing() const;
 
-  // 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(uint32_t bitrate_bps,
-                        size_t packet_size,
-                        int64_t now_ms);
+  // Initializes a new probing session.
+  // Returns true on success, false on failure.
+  bool InitiateProbing(uint32_t bitrate_bps,
+                       const int* multipliers,
+                       int multiplier_count);
 
   // Returns the number of milliseconds until the next packet should be sent to
   // get accurate probing.
@@ -50,24 +62,12 @@ 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.
-  void PacketSent(int64_t now_ms, size_t packet_size);
+  // Notifies the prober that a probe packet has been sent, which helps the
+  // prober move to the next packet in a probe.
+  // Returns |probing_state_| after the call.
+  State 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;
@@ -78,7 +78,7 @@ class BitrateProber {
   // 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.