Implement periodic bandwidth probing in application-limited region.

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 ee50f2e4165145b3736a5c31c82dfbcdd68ea677..5c2ec8df15049e15bd1fa63c4c88e70be8a9fe20 100644
--- a/webrtc/modules/pacing/paced_sender.h
+++ b/webrtc/modules/pacing/paced_sender.h
@@ -120,12 +120,13 @@ class PacedSender : public Module, public RtpPacketSender {
   // packets in the queue, given the current size and bitrate, ignoring prio.
   virtual int64_t ExpectedQueueTimeMs() const;
 
-  // Application Limited Region refers to operating in a state where the
+  // Returns time in milliseconds when application-limited regions started or
+  // zero if the sender is currently not application-limited.
+  //
+  // Application Limited Region (ALR) refers to operating in a state where the
   // traffic on network is limited due to application not having enough
   // traffic to meet the current channel capacity.
-  //
-  // Returns true if network is currently application-limited.
-  bool InApplicationLimitedRegion() const;
+  virtual int64_t GetApplicationLimitedRegionStartTime() const;
 
   // Returns the average time since being enqueued, in milliseconds, for all
   // packets currently in the pacer queue, or 0 if queue is empty.