Zero distortion skip for chroma RDO.
Zero distortion skip for chroma RDO.

Tested on this clip: https://gitlab.freedesktop.org/wayland/weston/issues/265

Before:

$ time target/release/rav1e ~/Downloads/pipewire-gtksink.y4m -o /dev/null --tiles 4
1920x1200 @ 30/1 fps
encoded 346 frames, 0.792 fps, 155.85 Kb/s
Key Frames:      4    avg size:   41038 B
Inter:         342    avg size:     176 B
Intra Only:      0    avg size:       0 B
Switch:          0    avg size:       0 B

After:

$ time target/release/rav1e ~/Downloads/pipewire-gtksink.y4m -o /dev/null --tiles 4
1920x1200 @ 30/1 fps
encoded 346 frames, 1.126 fps, 153.93 Kb/s
Key Frames:      4    avg size:   41038 B
Inter:         342    avg size:     168 B
Intra Only:      0    avg size:       0 B
Switch:          0    avg size:       0 B

https://beta.arewecompressedyet.com/?job=all_skip_modes%402019-07-22T23%3A48%3A01.955Z&job=chroma_reverse_order%402019-07-22T01%3A47%3A48.466Z

chroma_reverse_order@2019-07-22T01:47:48.466Z -> all_skip_modes@2019-07-22T23:48:01.955Z

   PSNR | PSNR Cb | PSNR Cr | PSNR HVS |    SSIM | MS SSIM | CIEDE 2000
-0.0043 |  0.0003 | -0.0135 |  -0.0045 | -0.0111 | -0.0119 |    -0.0308

xiph/rav1e,xiph/rav1e