Bug 939896 part 1: Introduce a FlexLine object, which manages a nsTArray of FlexItems on a single line in a flex container. r=mats
Bug 939896 part 2: Make ComputeLineCrossSize take a FlexLine. r=mats
Bug 939896 part 3a: Make FlexItem compute its own baseline offset from cross-start edge (and support bottom-to-top cross axis). r=mats
Bug 939896 part 3b: Keep track of line cross-size and baseline-alignment offset in FlexLine instead of in (more ephemeral) SingleLineCrossAxisPositionTracker. r=mats
Bug 939896 part 4: Move PositionItemInCrossAxis to live on FlexLine, and make it position all the line's items. r=mats
Bug 939896 part 5: Move PositionItemInMainAxis to live on FlexLine, and make it position all the line's items. r=mats
Bug 939896 part 6: Make ComputeFlexContainerMainSize take a FlexLine. r=mats
Bug 939896 part 7: Move ResolveFlexibleLengths() to live on FlexLine. r=mats
Bug 939896 part 8: Make FlexLine store the sums of its items' hypothetical inner & outer main sizes. r=mats
Bug 939896 part 9: Use cached sums of flexbox inner/outer main sizes in ResolveFlexibleLengths, and rename a variable. r=mats