Wire up experiment for improved screenshare bwe.

webrtc/modules/pacing/alr_detector.h

Index: webrtc/modules/pacing/alr_detector.h
diff --git a/webrtc/modules/pacing/alr_detector.h b/webrtc/modules/pacing/alr_detector.h
index d8870ff04bb14d783e803c041041c9b4fe066506..087e444da1e886d1d642ee1e4aa25d22bd99e046 100644
--- a/webrtc/modules/pacing/alr_detector.h
+++ b/webrtc/modules/pacing/alr_detector.h
@@ -11,6 +11,7 @@
 #ifndef WEBRTC_MODULES_PACING_ALR_DETECTOR_H_
 #define WEBRTC_MODULES_PACING_ALR_DETECTOR_H_
 
+#include "webrtc/base/optional.h"
 #include "webrtc/base/rate_statistics.h"
 #include "webrtc/common_types.h"
 #include "webrtc/modules/pacing/paced_sender.h"
@@ -25,6 +26,7 @@ namespace webrtc {
 // AlrDetector provides a signal that can be utilized to adjust
 // estimate bandwidth.
 // Note: This class is not thread-safe.
+
 class AlrDetector {
  public:
   AlrDetector();
@@ -39,9 +41,28 @@ class AlrDetector {
   // started or empty result if the sender is currently not application-limited.
   rtc::Optional<int64_t> GetApplicationLimitedRegionStartTime() const;
 
+  struct AlrExperimentSettings {
+    float pacing_factor = PacedSender::kDefaultPaceMultiplier;
+    int64_t max_paced_queue_time = PacedSender::kMaxQueueLengthMs;
+    int alr_start_usage_percent = kDefaultAlrStartUsagePercent;
+    int alr_end_usage_percent = kDefaultAlrEndUsagePercent;
+  };
+  static rtc::Optional<AlrExperimentSettings> ParseAlrSettingsFromFieldTrial();
+
+  // Sent traffic percentage as a function of network capacity used to determine
+  // application-limited region. ALR region start when bandwidth usage drops
+  // below kAlrStartUsagePercent and ends when it raises above
+  // kAlrEndUsagePercent. NOTE: This is intentionally conservative at the moment
+  // until BW adjustments of application limited region is fine tuned.
+  static constexpr int kDefaultAlrStartUsagePercent = 60;
+  static constexpr int kDefaultAlrEndUsagePercent = 70;
+  static const char* kScreenshareProbingBweExperimentName;
+
  private:
+  int alr_start_usage_percent_;
+  int alr_end_usage_percent_;
   RateStatistics rate_;
-  int estimated_bitrate_bps_ = 0;
+  int estimated_bitrate_bps_;
 
   // Non-empty in ALR state.
   rtc::Optional<int64_t> alr_started_time_ms_;