Implement periodic bandwidth probing in application-limited region.

webrtc/modules/pacing/paced_sender.cc

Index: webrtc/modules/pacing/paced_sender.cc
diff --git a/webrtc/modules/pacing/paced_sender.cc b/webrtc/modules/pacing/paced_sender.cc
index 445d116ed709154d3dbe52c99d4a6db822f62cd1..00523e61b7676a5cd10cfe22a6c83516927ac782 100644
--- a/webrtc/modules/pacing/paced_sender.cc
+++ b/webrtc/modules/pacing/paced_sender.cc
@@ -343,9 +343,10 @@ int64_t PacedSender::ExpectedQueueTimeMs() const {
                               pacing_bitrate_kbps_);
 }
 
-bool PacedSender::InApplicationLimitedRegion() const {
+rtc::Optional<int64_t> PacedSender::GetApplicationLimitedRegionStartTime()
+    const {
   CriticalSectionScoped cs(critsect_.get());
-  return alr_detector_->InApplicationLimitedRegion();
+  return alr_detector_->GetApplicationLimitedRegionStartTime();
 }
 
 size_t PacedSender::QueueSizePackets() const {