[css-regions] Expose info about line breaks, overflow to JS

Hey,
given that there is still so much disagreement with CSS Regions on the part
of Opera, Firefox and lately also from Chrome, based on supposed
performance issues, it was mentioned that the rendering engines, according
to the view of some, should just be the basis of applications that can then
take care of fragmentation.

In order to be able to do that half-way efficiently, it would be an
advantage for the Javascript to know where fragmentation occurs: 1. line
breaks and 2. how much of a node could be rendered without causing overflow.

With this info (which the browser should have anyway) available in
Javascript it should be a lot less time spent on trying to recreate what
happens when creating the javascript.

-- 
Johannes Wilm
Fidus Writer
http://www.fiduswriter.com