MathML:Cleanup

[DONE] DOM updates

See bug 744783.

[fredw]: The known issues are fixed.

[DONE] GFX Glue Layer Removal

An important step for MathML is bug 663740, which will allow to start the work on OpenType MATH table, to support more MathML fonts. More generally, see bug 430829, Gfx_glue_layer_removal and the thread on mozilla.dev.tech.gfx.

[fredw]: the main refactoring bug 663740 is done.

[DONE] Attribute Mapping into Style

We are using private attributes and pre-defined rules in mathml.css to map some MathML attributes into CSS. This approach shows its limits for length attributes (bug 330964) and exposes unwanted attributes to the DOM (bug 527201). We should rewrite this in a cleaner way (bug 69409).

[fredw]: the private attributes have been removed.

[DONE] Width Computation

Our layout engine still has some problems with width computation. See for example bug 459363 or bug 415413. Should we find a better algorithm?

[fredw]: the main preferred width bugs are fixed.

Box Model for MathML

The <math> element is implemented as an inline-box, but this gives an incorrect height computation (bug 219873). We should also allow linebreaking inside <mrow>'s, as specified by the rules of MathML 3 (bug 508120).