The syntax of the 'justify-items' property accepts a new 'legacy' value,
replacing the 'auto' value which is now parsed as invalid.

https://github.com/w3c/csswg-drafts/issues/1318

This change affects also to the 'place-items' shorthand, which doesn't
accept 'auto' and, for the time being, neither 'legacy'.

Link to the intent-to-ship-and-remove request:

https://groups.google.com/a/chromium.org/d/msgid/blink-dev/552753c1-9b2f-bb01-4fed-2ae621f2398e%40igalia.com?utm_medium=email&utm_source=footer

Bug: 726147, 726148
Change-Id: I219de66b813d350fe33f00a1d4369bed8e9a2350
Reviewed-on: https://chromium-review.googlesource.com/903162
Commit-Queue: Javier Fernandez <[email protected]>
Reviewed-by: Christian Biesinger <[email protected]>
Reviewed-by: Darren Shen <[email protected]>
Cr-Commit-Position: refs/heads/master@{#535593}