TransportFeedback must be able to start with dropped packets.

webrtc/modules/rtp_rtcp/source/rtcp_packet/transport_feedback_unittest.cc

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 341 matching lines @@
 
     EXPECT_NEAR(expected_time, accumulated_delta,
                 TransportFeedback::kDeltaScaleFactor / 2);
   }
 }
 
 TEST(RtcpPacketTest, TransportFeedback_Limits) {
   // Sequence number wrap above 0x8000.
   std::unique_ptr<TransportFeedback> packet(new TransportFeedback());
   packet->WithBase(0, 0);
+  EXPECT_TRUE(packet->WithReceivedPacket(0x0, 0));
   EXPECT_TRUE(packet->WithReceivedPacket(0x8000, 1000));
 
   packet.reset(new TransportFeedback());
   packet->WithBase(0, 0);
+  EXPECT_TRUE(packet->WithReceivedPacket(0x0, 0));
   EXPECT_FALSE(packet->WithReceivedPacket(0x8000 + 1, 1000));
 
   // Packet status count max 0xFFFF.
   packet.reset(new TransportFeedback());
   packet->WithBase(0, 0);
+  EXPECT_TRUE(packet->WithReceivedPacket(0x0, 0));
   EXPECT_TRUE(packet->WithReceivedPacket(0x8000, 1000));
   EXPECT_TRUE(packet->WithReceivedPacket(0xFFFF, 2000));
   EXPECT_FALSE(packet->WithReceivedPacket(0, 3000));
 
   // Too large delta.
   packet.reset(new TransportFeedback());
   packet->WithBase(0, 0);
   int64_t kMaxPositiveTimeDelta = std::numeric_limits<int16_t>::max() *
                                   TransportFeedback::kDeltaScaleFactor;
   EXPECT_FALSE(packet->WithReceivedPacket(
@@ skipping 90 matching lines @@
     rtc::Buffer serialized_packet = feedback.Build();
     std::unique_ptr<TransportFeedback> deserialized_packet =
         TransportFeedback::ParseFrom(serialized_packet.data(),
                                      serialized_packet.size());
     EXPECT_TRUE(deserialized_packet.get() != nullptr);
   }
 }
 
 }  // namespace
 }  // namespace webrtc