Distortion metric that is currently used for CDEF is also used for
distortion of luma channel during RDO-based mode decision.

This experiment works on the top of 'dist-8x8' experiment.

The BD-Rate change by this experiment for three frames of
objective-1-fast in AWCY is:

  PSNR | PSNR Cb | PSNR Cr | PSNR HVS |    SSIM | MS SSIM | CIEDE 2000
1.1589 | -2.0036 | -1.9620 |  -0.0076 | -1.4145 | -1.4561 |    -0.6410

Change-Id: I1142fe2f186f4ed86e4d33468e00b84e30b20233