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 993c6cd07edde5b87d2ea5f4b061dc5c183c5a40..194ddbccf83c305e221bae1771c2584b4cf64961 100644
--- a/webrtc/modules/pacing/alr_detector.cc
+++ b/webrtc/modules/pacing/alr_detector.cc
@@ -10,6 +10,7 @@
 
 #include "webrtc/modules/pacing/alr_detector.h"
 
+#include <map>
 #include <string>
 
 #include "webrtc/rtc_base/checks.h"
@@ -81,6 +82,16 @@ AlrDetector::ParseAlrSettingsFromFieldTrial(const char* experiment_name) {
   rtc::Optional<AlrExperimentSettings> ret;
   std::string group_name = field_trial::FindFullName(experiment_name);
 
+  static std::map<const char*,
+                  rtc::Optional<AlrDetector::AlrExperimentSettings>>
+      computed_results;
+
+  auto it = computed_results.find(experiment_name);
+  if (it != computed_results.end()) {
+    return it->second;
+  }
+  computed_results[experiment_name] = ret;
+
   const std::string kIgnoredSuffix = "_Dogfood";
   if (group_name.rfind(kIgnoredSuffix) ==
       group_name.length() - kIgnoredSuffix.length()) {
@@ -91,11 +102,12 @@ AlrDetector::ParseAlrSettingsFromFieldTrial(const char* experiment_name) {
     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 ALR experiment settings: "
                     "pacing factor: "
@@ -106,11 +118,13 @@ AlrDetector::ParseAlrSettingsFromFieldTrial(const char* experiment_name) {
                  << ", 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;
   } else {
     LOG(LS_INFO) << "Failed to parse ALR experiment: " << experiment_name;
   }
 
+  computed_results[experiment_name] = ret;
   return ret;
 }