Reset NACK/ACK list when parsing a new RTCP packet.

media/cast/net/rtcp/rtcp_utility.cc

Index: media/cast/net/rtcp/rtcp_utility.cc
diff --git a/media/cast/net/rtcp/rtcp_utility.cc b/media/cast/net/rtcp/rtcp_utility.cc
index 667026e012d87e27cb3a87266352ba71be603b8f..99717c5ad054e475239fda0b00af2386f6aef698 100644
--- a/media/cast/net/rtcp/rtcp_utility.cc
+++ b/media/cast/net/rtcp/rtcp_utility.cc
@@ -322,6 +322,8 @@ bool RtcpParser::ParseFeedbackCommon(base::BigEndianReader* reader,
   // Please note, this frame_id is still only 8-bit!
   cast_message_.ack_frame_id = last_frame_id;
 
+  cast_message_.missing_frames_and_packets.clear();
+  cast_message_.received_later_frames.clear();
   for (size_t i = 0; i < number_of_lost_fields; i++) {
     uint8_t frame_id;
     uint16_t packet_id;