Bug 841827: Mark flex container frame as having a relative height, if it's abspos w/ auto-height and top,bottom both set. r=dbaron

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rename : layout/reftests/flexbox/flexbox-dyn-changeFrameWidth-1-iframe.html => layout/reftests/flexbox/flexbox-dyn-changeFrameWidth-4-iframe.html
rename : layout/reftests/flexbox/flexbox-dyn-changeFrameWidth-1-ref.xhtml => layout/reftests/flexbox/flexbox-dyn-changeFrameWidth-4-ref.xhtml
rename : layout/reftests/flexbox/flexbox-dyn-changeFrameWidth-1.xhtml => layout/reftests/flexbox/flexbox-dyn-changeFrameWidth-4.xhtml