Update from https://crrev.com/304418

net/quic/congestion_control/hybrid_slow_start_test.cc

Index: net/quic/congestion_control/hybrid_slow_start_test.cc
diff --git a/net/quic/congestion_control/hybrid_slow_start_test.cc b/net/quic/congestion_control/hybrid_slow_start_test.cc
index dd74933840f10bce15ad3367b3b7dfebc9560ddb..bcdf8d900bccd60a80d001a2982505bef5d298cc 100644
--- a/net/quic/congestion_control/hybrid_slow_start_test.cc
+++ b/net/quic/congestion_control/hybrid_slow_start_test.cc
@@ -54,26 +54,33 @@ TEST_F(HybridSlowStartTest, AckTrain) {
   // At a typical RTT 60 ms, assuming that the inter arrival timestamp is 1 ms,
   // we expect to be able to send a burst of 30 packet before we trigger the
   // ack train detection.
-  const int kMaxLoopCount = 5;
-  QuicPacketSequenceNumber sequence_number = 2;
-  QuicPacketSequenceNumber end_sequence_number = 2;
-  for (int burst = 0; burst < kMaxLoopCount; ++burst) {
+  // Run this test for both enabled and disabled ack train detection.
+  for (int i = 0; i < 2; ++i) {
+    const bool ack_train_detection = (i == 1);
+    slow_start_->set_ack_train_detection(ack_train_detection);
+
+    const int kMaxLoopCount = 5;
+    QuicPacketSequenceNumber sequence_number = 2;
+    QuicPacketSequenceNumber end_sequence_number = 2;
+    for (int burst = 0; burst < kMaxLoopCount; ++burst) {
+      slow_start_->StartReceiveRound(end_sequence_number);
+      do {
+        clock_.AdvanceTime(one_ms_);
+        EXPECT_FALSE(slow_start_->ShouldExitSlowStart(rtt_, rtt_, 100));
+      } while (!slow_start_->IsEndOfRound(sequence_number++));
+      end_sequence_number *= 2;  // Exponential growth.
+    }
     slow_start_->StartReceiveRound(end_sequence_number);
-    do {
+
+    for (int n = 0;
+         n < 29 && !slow_start_->IsEndOfRound(sequence_number++); ++n) {
       clock_.AdvanceTime(one_ms_);
       EXPECT_FALSE(slow_start_->ShouldExitSlowStart(rtt_, rtt_, 100));
-    }  while (!slow_start_->IsEndOfRound(sequence_number++));
-    end_sequence_number *= 2;  // Exponential growth.
-  }
-  slow_start_->StartReceiveRound(end_sequence_number);
-
-  for (int n = 0;
-       n < 29 && !slow_start_->IsEndOfRound(sequence_number++); ++n) {
+    }
     clock_.AdvanceTime(one_ms_);
-    EXPECT_FALSE(slow_start_->ShouldExitSlowStart(rtt_, rtt_, 100));
+    EXPECT_EQ(ack_train_detection,
+              slow_start_->ShouldExitSlowStart(rtt_, rtt_, 100));
   }
-  clock_.AdvanceTime(one_ms_);
-  EXPECT_TRUE(slow_start_->ShouldExitSlowStart(rtt_, rtt_, 100));
 }
 
 TEST_F(HybridSlowStartTest, Delay) {