Piggybacking simulcast id and ALR experiment id into video content type extension.

webrtc/modules/pacing/alr_detector.cc

Index: webrtc/modules/pacing/alr_detector.cc
diff --git a/webrtc/modules/pacing/alr_detector.cc b/webrtc/modules/pacing/alr_detector.cc
index 93752cf751395d99db60e146ef87f4b0558e4dcb..5d3cf7e1bbb3cef3430fdec793b805acb4409ce1 100644
--- a/webrtc/modules/pacing/alr_detector.cc
+++ b/webrtc/modules/pacing/alr_detector.cc
@@ -23,6 +23,9 @@ namespace webrtc {
 const char* AlrDetector::kScreenshareProbingBweExperimentName =
     "WebRTC-ProbingScreenshareBwe";
 
+const char* AlrDetector::kScreenshareProbingBweExperimentNameOnReceiveSide =
+    "WebRTC-ProbingScreenshareBwe-Receive";
+
 AlrDetector::AlrDetector()
     : bandwidth_usage_percent_(kDefaultAlrBandwidthUsagePercent),
       alr_start_budget_level_percent_(kDefaultAlrStartBudgetLevelPercent),
@@ -82,11 +85,12 @@ AlrDetector::ParseAlrSettingsFromFieldTrial() {
     return ret;
 
   AlrExperimentSettings settings;
-  if (sscanf(group_name.c_str(), "%f,%" PRId64 ",%d,%d,%d",
+  if (sscanf(group_name.c_str(), "%f,%" PRId64 ",%d,%d,%d,%d",
              &settings.pacing_factor, &settings.max_paced_queue_time,
              &settings.alr_bandwidth_usage_percent,
              &settings.alr_start_budget_level_percent,
-             &settings.alr_stop_budget_level_percent) == 5) {
+             &settings.alr_stop_budget_level_percent,
+             &settings.group_id) == 6) {
     ret.emplace(settings);
     LOG(LS_INFO) << "Using screenshare ALR experiment settings: "
                     "pacing factor: "
@@ -97,7 +101,8 @@ AlrDetector::ParseAlrSettingsFromFieldTrial() {
                  << ", ALR end budget level percent: "
                  << settings.alr_start_budget_level_percent
                  << ", ALR end budget level percent: "
-                 << settings.alr_stop_budget_level_percent;
+                 << settings.alr_stop_budget_level_percent
+                 << ", ALR experiment group ID: " << settings.group_id;
   }
 
   return ret;