[css-grid] Implement repeat(auto-fit)
The auto-fit keyword works exactly as the already implemented auto-fill
except that all empty tracks collapse (became 0px). Absolutely
positioned items do not participate on the layout of the grid so they are
not considered (a grid with only absolutely positioned items is considered
an empty grid).
Whenever a track collapses the gutters on either side do also collapse. When a
collapsed track’s gutters collapse, they coincide exactly. If one side of a
collapsed track does not have a gutter then collapsing its gutters results in no
gutter on either “side” of the collapsed track.
Uncommented the auto-fit cases from Mozilla tests. They have to be adapted
as the reftest machinery requires all the content to be rendered in the
original 800x600 viewport.
BUG=589460
Review-Url: https://codereview.chromium.org/2080643002
Cr-Commit-Position: refs/heads/master@{#405849}
26 files changed
