Make PayloadRouter own the picture id and tl0 pic idx sequences.

It previously owned only the picture id and only in the
WebRTC-VP8-Forced-Fallback-Encoder-v2 experiment.

Moving responsibility to PayloadRouter ensures that  both
picture id and tl0 idx are continuous over codec changes,
as required by the specs for VP8 and VP9 over RTP.

Bug: webrtc:8830
Change-Id: Ie77356dfec6d1e372b6970189e4c3888451920e6
Reviewed-on: https://webrtc-review.googlesource.com/61640
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22448}

modules/video_coding/include/video_codec_interface.h

@@ -28,23 +28,28 @@ class RTPFragmentationHeader;  // forward declaration
 // Note: if any pointers are added to this struct, it must be fitted
 // with a copy-constructor. See below.
 struct CodecSpecificInfoVP8 {
+  // TODO(nisse): Delete, set by PayloadRouter.
   int16_t pictureId;  // Negative value to skip pictureId.
   bool nonReference;
   uint8_t simulcastIdx;
   uint8_t temporalIdx;
   bool layerSync;
+  // TODO(nisse): Delete, set by PayloadRouter.
   int tl0PicIdx;  // Negative value to skip tl0PicIdx.
   int8_t keyIdx;  // Negative value to skip keyIdx.
 };
 
 struct CodecSpecificInfoVP9 {
+  // TODO(nisse): Delete, set by PayloadRouter.
   int16_t picture_id;  // Negative value to skip pictureId.
 
+  bool first_frame_in_picture;  // First frame, increment picture_id.
   bool inter_pic_predicted;  // This layer frame is dependent on previously
                              // coded frame(s).
   bool flexible_mode;
   bool ss_data_available;
 
+  // TODO(nisse): Delete, set by PayloadRouter.
   int tl0_pic_idx;  // Negative value to skip tl0PicIdx.
   uint8_t temporal_idx;
   uint8_t spatial_idx;