It turns out part 10 was actually needed, but Bug 1449838 had a significantly
better version of what that code does that was easy enough to backport to what
we have. As far as I can tell, this passes the relevant reftests now.
This implements flexbox layout for the gap properties without the refactoring work performed on `nsFlexContainerFrame`.
Partially based on https://bugzilla.mozilla.org/show_bug.cgi?id=1398483 and https://bugzilla.mozilla.org/show_bug.cgi?id=1454822
This excludes the second part of bug 1454822, the width caching implementation, because it is out of scope and currently causes unstable layout with `writing-mode: vertical-lr` (see bug 1709937).
Since these are just interpreted comments, there's 0 impact on actual code.
This removes all lines that match /* vim: set(.*)tw=80: */ with S&R -- there are
a few others scattered around which will be removed manually in a second part.
https://bugzilla.mozilla.org/show_bug.cgi?id=1547792
Aspect Ratio handling simplified by using floating point integers:
- Multiplication of value (or inverse value) to a known side for Scaling
- No unequal equal values such as "4/3" vs "8/6" vs "20/15"
- Truly "Empty" aspect ratios, even if one dimension is not 0
Part 1: Remove current table item, as it's never set.
Part 2: Get rid of generic table painting code, and handle each class separately.
Part 4: Hoist outline skipping into col(group) frame code.
Part 5: Skip box-shadow for table column and column groups.
Part 6: Store column and column group backgrounds separately, and then append them before the rest of the table contents.
Part 7: Pass rects in display list coordinates to AppendBackgroundItemsToTop.
Part 8: Create column and column group background display items as part of the cell's BuildDisplayList.
Part 9: Used cached values instead of calling nsDisplayListBuilder::ToReferenceFrame when possible, since it can be expensive when the requested frame isn't the builder's current frame.
Part 10: Make sure we build display items for table parts where only the normal position is visible, since we may need to create background items for ancestors at that position.
Part 11: Create an AutoBuildingDisplayList when we create background items for table columns and column groups, so that we initialize the invalidation state correctly.