Previously, the width and height of grid items were set to match the
size of the grid area they belonged to. With this change, if a grid
item has preferred width or height specified to not "auto" value it
will be resolved using grid area as containing block and used instead.
1. Stop using -1 to indicate infinity value of growth limit. Just use
INFINITY for that.
2. More complete implementation of "Expand Flexible Tracks" step.
3. Return AvailableSize from get_free_space: spec says that this
function can return indefinite size and it is ok.
The file gap.html, which previously had multiple grid tests, has now
been divided into smaller files, each containing only one grid test.
It is going to make it easier to identify what inputs have been
affected by changes in layout code.
The file template-areas.html, which previously had multiple grid tests,
has now been divided into smaller files, each containing only one grid
test. It is going to make it easier to identify what inputs have been
affected by changes in layout code.
Also this change removes parts of template-areas.html that we can't
layout correctly yet.
This fixes a bug that was seen when a combination of the grid having
been floated with `float: left` and a `minmax()` column size were used.
The issue was that a grid track size should be considered intrinsically
sized if both the min and max sizes are intrinsic, not just one of them.
