https://drafts.csswg.org/css-flexbox-1/#flex-baselines The current implementation of getBaselineChild does not take into consideration the writing mode or flex direction when determining which flex item to use for the flex container's baseline. This leads to many failures in the css/css-flexbox/alignment/flex-align-baseline-flex-* WPT tests. This bugzilla issue should serve as an umbrella for all of the incremental patches that will be added to rework the function implementation to more closely align to the spec.
<rdar://problem/113765715>
Renaming the bug to mention that we should be using the flex line structure instead since that's really the central issue in the code