Add an experiment for stricter pacing and ALR probing.

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 7e630970e6345f31fdb399bf322525c071eff26e..250002d9fb1b91121d6bead5432485ceb10144a9 100644
--- a/webrtc/modules/pacing/alr_detector.h
+++ b/webrtc/modules/pacing/alr_detector.h
@@ -48,7 +48,8 @@ class AlrDetector {
     int alr_start_budget_level_percent = kDefaultAlrStartBudgetLevelPercent;
     int alr_stop_budget_level_percent = kDefaultAlrStopBudgetLevelPercent;
   };
-  static rtc::Optional<AlrExperimentSettings> ParseAlrSettingsFromFieldTrial();
+  static rtc::Optional<AlrExperimentSettings> ParseAlrSettingsFromFieldTrial(
+      const char* experiment_name);
 
   // Sent traffic percentage as a function of network capacity used to determine
   // application-limited region. ALR region start when bandwidth usage drops
@@ -59,6 +60,7 @@ class AlrDetector {
   static constexpr int kDefaultAlrStartBudgetLevelPercent = 80;
   static constexpr int kDefaultAlrStopBudgetLevelPercent = 50;
   static const char* kScreenshareProbingBweExperimentName;
+  static const char* kStrictPacingAndProbingExperimentName;
 
   void UpdateBudgetWithElapsedTime(int64_t delta_time_ms);
   void UpdateBudgetWithBytesSent(size_t bytes_sent);