* Add snapshot tests for interitem and interline spacings of stack spec
* Improve comment
* Make sure item spacings are properly considered and reset on new lines, snapshot tests included
- Avoid returning a NaN flexShrinkAdjustment.
- Bail early (instead of assert) if a line has a positive `flexFactorSum` but then no flexible item can be found via flex adjustments, for example because the flexible items have zero size.
- Continue flexing other lines when one line is inflexible.
- Add unit test for the first 2 fixes.
* Clean up snapshot test cases:
- Drop 32bit snapshots
- Update iOS 9 snapshots and move some others to the correct directory
- Remove `setUp` overrides in subclasses of `ASLayoutSpecSnapshotTestCase` that set `recordMode` flag. Doing so in multiple places make it difficult to enable/dis
able the flag for all layout spec test cases. It can always be overridden locally if need
to.
- Fix BUCK build
* Fix testThatOnDidLoadThrowsIfCalledOnLoadedOffMain of ASDisplayNodeTests
