Remove WebRTC-AddPacingToCongestionWindowPushback field trial

This trial was introduced to include the pacing buffer size in the congestion window pushback. The codebase now assumes this behavior as default, so the field trial is no longer needed.

Also, add back unittests that were removed from the build in https://webrtc-review.git.corp.google.com/c/src/+/490780/13/modules/congestion_controller/BUILD.gn

Bug: webrtc:42221607
Change-Id: Ie04944122b595946ca5fbd33bf89f7fc8fa83082
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/458042
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Fredrik Solenberg <solenberg@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48297}

experiments/field_trials.py

diff --git a/experiments/field_trials.py b/experiments/field_trials.py
index 2038962..791ba77 100755
--- a/experiments/field_trials.py
+++ b/experiments/field_trials.py
@@ -281,9 +281,6 @@
     FieldTrial('WebRTC-AddNetworkCostToVpn',
                42223280,
                date(2024, 4, 1)),
-    FieldTrial('WebRTC-AddPacingToCongestionWindowPushback',
-               42220204,
-               date(2024, 4, 1)),
     FieldTrial('WebRTC-AdjustOpusBandwidth',
                42233664,
                date(2024, 4, 1)),
@@ -932,7 +929,7 @@
 ])  # yapf: disable
 
 POLICY_EXEMPT_FIELD_TRIALS_DIGEST: str = \
-    '8470357338d133964bb56ea554cc1e824b2651f3'
+    'b41ff32cc255517f1ba5add2a601453c5fc9e7c3'
 
 REGISTERED_FIELD_TRIALS: FrozenSet[FieldTrial] = ACTIVE_FIELD_TRIALS.union(
     POLICY_EXEMPT_FIELD_TRIALS)

modules/congestion_controller/BUILD.gn

diff --git a/modules/congestion_controller/BUILD.gn b/modules/congestion_controller/BUILD.gn
index b3b29db..54f47da 100644
--- a/modules/congestion_controller/BUILD.gn
+++ b/modules/congestion_controller/BUILD.gn
@@ -87,6 +87,12 @@
     deps = [
       ":receive_side_congestion_controller_unittest",
       ":remb_throttler_unittest",
+      "goog_cc:goog_cc_unittests",
+      "goog_cc_scream_network_controller:goog_cc_scream_network_controller_unittests",
+      "pcc:pcc_unittests",
+      "rtp:congestion_controller_unittests",
+      "scream:scream_unittests",
+      "scream/test:cc_feedback_generator_unittests",
     ]
   }
 }

modules/congestion_controller/goog_cc/congestion_window_pushback_controller.cc

diff --git a/modules/congestion_controller/goog_cc/congestion_window_pushback_controller.cc b/modules/congestion_controller/goog_cc/congestion_window_pushback_controller.cc
index d3b791d..5870923 100644
--- a/modules/congestion_controller/goog_cc/congestion_window_pushback_controller.cc
+++ b/modules/congestion_controller/goog_cc/congestion_window_pushback_controller.cc
@@ -21,9 +21,7 @@
 
 CongestionWindowPushbackController::CongestionWindowPushbackController(
     const FieldTrialsView& key_value_config)
-    : add_pacing_(key_value_config.IsEnabled(
-          "WebRTC-AddPacingToCongestionWindowPushback")),
-      min_pushback_target_bitrate_bps_(
+    : min_pushback_target_bitrate_bps_(
           RateControlSettings(key_value_config)
               .CongestionWindowMinPushbackTargetBitrateBps()),
       current_data_window_(RateControlSettings(key_value_config)
@@ -46,9 +44,7 @@
     uint32_t bitrate_bps) {
   if (!current_data_window_ || current_data_window_->IsZero())
     return bitrate_bps;
-  int64_t total_bytes = outstanding_bytes_;
-  if (add_pacing_)
-    total_bytes += pacing_bytes_;
+  int64_t total_bytes = outstanding_bytes_ + pacing_bytes_;
   double fill_ratio =
       total_bytes / static_cast<double>(current_data_window_->bytes());
   if (fill_ratio > 1.5) {

modules/congestion_controller/goog_cc/congestion_window_pushback_controller.h

diff --git a/modules/congestion_controller/goog_cc/congestion_window_pushback_controller.h b/modules/congestion_controller/goog_cc/congestion_window_pushback_controller.h
index 208331f..9e04ae2 100644
--- a/modules/congestion_controller/goog_cc/congestion_window_pushback_controller.h
+++ b/modules/congestion_controller/goog_cc/congestion_window_pushback_controller.h
@@ -35,7 +35,6 @@
   void SetDataWindow(DataSize data_window);
 
  private:
-  const bool add_pacing_;
   const uint32_t min_pushback_target_bitrate_bps_;
   std::optional<DataSize> current_data_window_;
   int64_t outstanding_bytes_ = 0;

modules/congestion_controller/goog_cc/goog_cc_network_control_unittest.cc

diff --git a/modules/congestion_controller/goog_cc/goog_cc_network_control_unittest.cc b/modules/congestion_controller/goog_cc/goog_cc_network_control_unittest.cc
index aa6f2fc..b43a769 100644
--- a/modules/congestion_controller/goog_cc/goog_cc_network_control_unittest.cc
+++ b/modules/congestion_controller/goog_cc/goog_cc_network_control_unittest.cc
@@ -851,7 +851,7 @@
   EXPECT_GT(client->send_bandwidth().kbps(), kNewLinkCapacity.kbps() - 300);
 }
 
-TEST(GoogCcScenario, TargetRateReducedOnPacingBufferBuildupInTrial) {
+TEST(GoogCcScenario, TargetRateReducedOnPacingBufferBuildup) {
   const DataRate kLinkCapacity = DataRate::KilobitsPerSec(1000);
   const DataRate kStartRate = DataRate::KilobitsPerSec(1000);
 
@@ -864,8 +864,6 @@
     c->field_trials.Set("WebRTC-CongestionWindow",
                         "QueueSize:100,MinBitrate:30000");
     c->field_trials.Set("WebRTC-Video-Pacing", "factor:1.0");
-    c->field_trials.Set("WebRTC-AddPacingToCongestionWindowPushback",
-                        "Enabled");
     c->transport.rates.start_rate = kStartRate;
   });
   auto* route = s.CreateRoutes(