Update VP8 settings to avoid spending bitrate on static areas. PERF NOTE
Update VP8 settings to avoid spending bitrate on static areas. PERF NOTE

This CL changes the threshold where we consider a block to be static and
of sufficient quality to not spend bits/CPU encoding it.

Perf note: This change may result in a minor degradation of PSNR/SSIM
and available send bitrate. CPU usage and bitrate sent should however
be greately reduced.

BUG=webrtc:5015

Review URL: https://codereview.webrtc.org/1383533002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#10134}

ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc