PageDimension metric

[fbuchinger]

pageHeight: height of the page in pixels including scroll area (i.e. document.body.scrollHeight)
pageWidth: actual width of page content (idea: change window width and see if pageHeight changes
pageSize: pageHeight*pageWidth -> size in megapixels

[fbuchinger]

Two remarks:

• should it really be called "pageDimension" or better "blockDimension"? (layoutstats might be invoked on a grandchild of document.body, then it wouldn't measure scrollHeight of that element but not of the whole page)
• pageWidth could be calculated by using the text node bounding boxes mentioned in font metrics should consider text node area instead of character count #10 (page width ~ bbox(maxRight) - bbox(minLeft))