Bug 873806 - Part 1: Ensure non-display SVG text frames get reflowed. r=longsonr f=jwatt

--HG--
rename : layout/reftests/svg/text/clipPath-content.svg => layout/reftests/svg/text/clipPath-content-2.svg
rename : layout/reftests/svg/text/mask-content.svg => layout/reftests/svg/text/mask-content-2.svg
Bug 873806 - Part 2: Make descendants of non-display nsSVGForeignObjectFrame also non-display. r=longsonr
Bug 876831 - Only reflow nsSVGTextFrame2's anonymous block frame under ReflowSVG. r=bzbarsky,longsonr f=jwatt