Move SPS/PPS/IDR requirement from RtpFrameObject to PacketBuffer.

BUG=webrtc:8423

Change-Id: I0f0d59461afead700c20c9a2ed9b2bc991590b4a
Reviewed-on: https://webrtc-review.googlesource.com/15101
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Rasmus Brandt <brandtr@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20559}

modules/video_coding/packet_buffer.h

@@ -160,6 +160,10 @@ class PacketBuffer {
   std::set<uint16_t, DescendingSeqNumComp<uint16_t>> missing_packets_
       RTC_GUARDED_BY(crit_);
 
+  // Indicates if we should require SPS, PPS, and IDR for a particular
+  // RTP timestamp to treat the corresponding frame as a keyframe.
+  const bool sps_pps_idr_is_h264_keyframe_;
+
   mutable volatile int ref_count_ = 0;
 };