Actually apply all previous SetPixels changes.
If updateMipmaps is true, the mipmap levels are recalculated as well, using
the base level as a source. Usually you want to use true in all cases except when
you've modified the mip levels yourself using SetPixels.
This is a potentially expensive operation, so you'll want to change as many pixels
as possible between Apply calls.
See Also: SetPixels functions.