Fix off-by-one error in DCHECK in ProducerFec.

webrtc/modules/rtp_rtcp/source/producer_fec_unittest.cc

 /*
  *  Copyright (c) 2012 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 167 matching lines @@
                packet->header.header.timestamp,
                kRedPayloadType,
                packet->header.header.payloadType,
                red_packet.get(),
                true);  // Marker bit set.
   for (int i = 0; i < 10; ++i)
     EXPECT_EQ(i, red_packet->data()[kRtpHeaderSize + 1 + i]);
   delete packet;
 }
 
+TEST_F(ProducerFecTest, BuildRedPacketWithEmptyPayload) {
+  constexpr size_t kNumFrames = 1;
+  constexpr size_t kFrameId = 0;

[danilchap, 2016/09/01 07:59:17]

may be constexpr int kOffset = 0;
NextPacket name this parameter offset and use it as a random generator.
Doesn't feel related to Frame Id and definitely not a size_t.

Or, like in previous test do not introduce this constant since it is completely
irrelevant for this test.

[brandtr, 2016/09/01 09:29:18]

I'm not a fan of unnamed literals in the tests, but I still changed to that here
to avoid the confusion about what this offset means. The offset affects the
payload of the generated packets, and is typically used to separate the payloads
of different frames. Not really applicable here though.

About the type, I'd argue that it should be size_t in the signature of
NextPacket :)

+  constexpr size_t kPayloadLength = 0;
+
+  generator_.NewFrame(kNumFrames);
+  std::unique_ptr<test::RawRtpPacket> packet(
+      generator_.NextPacket(kFrameId, kPayloadLength));
+  std::unique_ptr<RedPacket> red_packet =
+      ProducerFec::BuildRedPacket(packet->data, packet->length - kRtpHeaderSize,
+                                  kRtpHeaderSize, kRedPayloadType);
+  EXPECT_EQ(packet->length + 1, red_packet->length());

[danilchap, 2016/09/01 07:59:17]

this + 1 is + kRedForFecHeaderLength?

[brandtr, 2016/09/01 09:29:18]

Yes, clarified.

+  VerifyHeader(packet->header.header.sequenceNumber,
+               packet->header.header.timestamp, kRedPayloadType,
+               packet->header.header.payloadType, red_packet.get(),
+               true);  // Marker bit set.
+}
+
 }  // namespace webrtc