This is useful for a forward change that will improve compression.
It splits the residual computation and the best predictor
selection.
The only downside is that more memory is allocated: we had 2
histograms before, we now have 14, but this is necessary for the
later change. Still, this is nothing compared to what is done
later in the pipeline in HistogramSetTotalSize where the number of
histograms created is the number of pixels in the subsampled image.
Change-Id: If03501a26f00462dd1809daa6e9314abd180945d
367ca938f1