[cssom-view] More getBoxQuads/convert*FromNode issues

What should getBoxQuads() on a table element return? Obvious options:
1) a quad for the "inner table box" (the box with the rows and columns,
which has the table border on it)
2) a quad for the "outer table box" (the box enclosing the inner table box
and any caption box, which has the table margins on it)
3) a quad for the "inner table box" and a quad for the caption box

For the analogous question with getClientRects(), Gecko currently does #3,
which is explicitly mandated as a special case in the CSSOM Views spec:
http://dev.w3.org/csswg/cssom-view/#dom-element-getclientrects
I think the rationale is that we want getBoundingClientRect() on a table to
include the caption area, but option #2 (which is what Chrome
getClientRects() does) doesn't match the box where the border is drawn and
doesn't give you a way to get the inner table box geometry).

In a way, the most logical thing to do for getBoxQuads would be to use the
inner table box for "content", "padding" and "border" boxes and use the
outer table box for "margin" boxes and ignore the caption altogether, but
that could still confuse authors. I'm not sure what to do, other than curse
tables.

Smaller issues: Should DOMPoint/DOMRect/DOMQuad constructors/attributes
allow unrestricted doubles? I think probably not.

What about list bullets: should they contribute quads to getQuadList? I
think anonymous decorations like list bullets probably should not.

Rob
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