Track maximum layer depth in a GOP
Track maximum layer depth in a GOP

Track the effective maximum layer depth in a given group of
pictures. Keep it in the GF_GROUP data structure.

Change-Id: If777c4e0f4a871c7226a91e3871f445e92f18b24

webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx