Refine interval for key frame boost calculation
Refine interval for key frame boost calculation

In the calculation of boost for key frames, increase number
of frames to be scanned based on the content nature.

Change-Id: Ia4533966a00055d0bec712e073d82d4bd1dc715a

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