Remove hardcoded kValueSizeBytes values from variable-length header extensions.

webrtc/modules/rtp_rtcp/source/flexfec_sender.cc

Index: webrtc/modules/rtp_rtcp/source/flexfec_sender.cc
diff --git a/webrtc/modules/rtp_rtcp/source/flexfec_sender.cc b/webrtc/modules/rtp_rtcp/source/flexfec_sender.cc
index 4aec05662fdaae852192570d7c9ca64dcb4a2776..03ca2b80b66b5ecc1af57e4061a1cc813674dbdb 100644
--- a/webrtc/modules/rtp_rtcp/source/flexfec_sender.cc
+++ b/webrtc/modules/rtp_rtcp/source/flexfec_sender.cc
@@ -147,8 +147,9 @@ std::vector<std::unique_ptr<RtpPacketToSend>> FlexfecSender::GetFecPackets() {
 }
 
 // The overhead is BWE RTP header extensions and FlexFEC header.
-size_t FlexfecSender::MaxPacketOverhead() const {
-  return rtp_header_extension_map_.GetTotalLengthInBytes() +
+size_t FlexfecSender::MaxPacketOverhead(
+    rtc::ArrayView<const RtpExtensionSize> extension_sizes) const {
+  return rtp_header_extension_map_.GetTotalLengthInBytes(extension_sizes) +

[brandtr, 2017/05/10 11:12:37]

I'm not familiar with the RID extension, but in this CL it looks like we don't
have to add it to the FlexFEC packets? Currently, we only register BWE header
extensions for FlexFEC:
https://cs.chromium.org/chromium/src/third_party/webrtc/modules/rtp_rtcp/sour...

Since this method is always called with a fixed input argument (from
rtp_sender_video.cc), can we move the call to 
rtp_header_extension_map_.GetTotalLengthInBytes(extension_sizes) to the ctor,
and have this method return a const member variable + kFlexfecMaxHeaderSize?

[erikvarga1, 2017/05/10 13:14:21]

Yeah, stream IDs aren't used here (or in padding packets), so Flexfec always
gets the same extension sizes.
I've moved the call into the constructor and also moved the FecExtensionSizes()
call to video_send_stream.cc (where the FlexfecSender is created).

[brandtr, 2017/05/10 14:36:27]

Thanks!

          kFlexfecMaxHeaderSize;
 }