Change QUIC to only ack every other packet when there are no losses

net/quic/quic_connection_test.cc

Index: net/quic/quic_connection_test.cc
diff --git a/net/quic/quic_connection_test.cc b/net/quic/quic_connection_test.cc
index c35918bc0f918b64bbc5668eeb33448d860435ad..39655d0fe2a73277fe37afeb4a0e347d0da83646 100644
--- a/net/quic/quic_connection_test.cc
+++ b/net/quic/quic_connection_test.cc
@@ -313,6 +313,11 @@ class TestPacketWriter : public QuicPacketWriter {
     return is_write_blocked_data_buffered_;
   }
 
+  // Resets the visitor's state by clearing out the headers and frames.
+  void Reset() {
+    visitor_.Reset();
+  }
+
   QuicPacketHeader* header() { return visitor_.header(); }
 
   size_t frame_count() const { return visitor_.frame_count(); }
@@ -2610,6 +2615,31 @@ TEST_F(QuicConnectionTest, SendDelayedAckOnSecondPacket) {
   EXPECT_FALSE(connection_.GetAckAlarm()->IsSet());
 }
 
+TEST_F(QuicConnectionTest, NoAckOnOldNacks) {
+  EXPECT_CALL(visitor_, OnSuccessfulVersionNegotiation(_));
+  // Drop one packet, triggering a sequence of acks.
+  ProcessPacket(2);
+  EXPECT_EQ(1u, writer_->frame_count());
+  EXPECT_TRUE(writer_->ack());
+  writer_->Reset();
+  ProcessPacket(3);
+  EXPECT_EQ(1u, writer_->frame_count());
+  EXPECT_TRUE(writer_->ack());
+  writer_->Reset();
+  ProcessPacket(4);
+  EXPECT_EQ(1u, writer_->frame_count());
+  EXPECT_TRUE(writer_->ack());
+  writer_->Reset();
+  ProcessPacket(5);
+  EXPECT_EQ(1u, writer_->frame_count());
+  EXPECT_TRUE(writer_->ack());
+  // Now only set the timer on the 6th packet, instead of sending another ack.
+  writer_->Reset();
+  ProcessPacket(6);
+  EXPECT_EQ(0u, writer_->frame_count());
+  EXPECT_TRUE(connection_.GetAckAlarm()->IsSet());
+}
+
 TEST_F(QuicConnectionTest, SendDelayedAckOnOutgoingPacket) {
   EXPECT_CALL(visitor_, OnSuccessfulVersionNegotiation(_));
   ProcessPacket(1);