PacketBuffer now can save how many times a packet has been nacked.

Also save size/max nack count in the FrameObject/RtpFrameObject.

BUG=webrtc:5514
R=stefan@webrtc.org

Review URL: https://codereview.webrtc.org/1988653002 .

Cr-Commit-Position: refs/heads/master@{#12863}

webrtc/modules/video_coding/packet.h

@@ -39,6 +39,7 @@ class VCMPacket {
   const uint8_t* dataPtr;
   size_t sizeBytes;
   bool markerBit;
+  int timesNacked;
 
   FrameType frameType;
   VideoCodecType codec;