They were previously taking up 9% of samples in a profile of PixelPaint
while selecting a mask, and as a result of moving them to the header
they were inlined, which effectively eliminated them from the profile.
The Mask class represents an opacity mask over a rectangular section
of an image, linking every pixel to an alpha value ranging from 0 (not
selected) to 255 (fully selected). "Partially selected" pixels can be
used to simulate anti-aliased curves.
This class will be used as the basis for the new non-rectangular
selection feature.
