Histogram in transformations -- adapt to masks

[Charles2]

I liked the innovation (PWP7?) that when applying a mask in a transformation that displays a histogram, it becomes a histogram for the masked area only. I hope it will carry into PWP8.

[jsachs]

I do have this on my list to put back in - some people preferred it the old way so it may be an option on a settings menu.

[frankpix]

Would it be possible to make it a selection button on the Transformation dialog, rather than in the setting? That way we could make our choice on the spot - do I want the histogram to reflect the entire image or just the masked part.