Comment 4 for bug 595428

The size of a text object is not font_size * string_len: think "mmm" vs. "iii".

I think we should find some library to do these calculations for us.
For instance, see how easy it is to find a bounding box inside a browser, using DOM and Javascript:
http://my.opera.com/MacDev_ed/blog/2009/01/21/getting-boundingbox-of-svg-elements