Rob, are you still working on this ? I'd like to assume this task it otherwise.

Eric, do you think we would need an "intent to implement" request for this issue ? As commented on  issue #726147  we would just need to rename 'auto' by the new CSS value defined in the CSS Box Alignment spec, 'legacy'. 

This change would imply changes in the CSS parsing logic, mainly, but the current layout behavior would be basically the same. 

BTW, I'll implement the same change in WebKit [1] as well; it seems that FF [2] is working on this too.

1- https://bugs.webkit.org/show_bug.cgi?id=172712
2- https://bugzilla.mozilla.org/show_bug.cgi?id=1363875

I expect we already have an Intent to Implement that covers the relevant spec. We should have an Intent to Ship for shipping the new functionality.

The CSS Box Alignment spec has to be implemented for each layout model, following the Partial Implementation rules:

https://drafts.csswg.org/css-align/#partial

We implemented this spec just for Grid, as part of the Grid's intent-to-implement. Flexbox already implemented it since most of it was already defined in the Flexbox spec itself. The spec is still in Partial Implementation status, since it has to be implemented for Block and Multi Column. 

Now, what we are trying to implement in this issue is more a "replacement" than a new implementation. The spec has changed so that the 'auto' CSS value has been renamed to "legacy", but the functionality is basically the same.

I'm not sure whether it's possible/convenient to implement it as a single operation or either I should sent first an intent-to-implement-and-ship for the new value and then and intent-deprecate-and-remove for the old one.
   

Hi Javier, sorry I never got around to this, feel free to take over, assinging to you.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/464de2c5b1f00abced98a1a705889046859f5948

commit 464de2c5b1f00abced98a1a705889046859f5948
Author: Javier Fernandez <jfernandez@igalia.com>
Date: Fri Feb 09 00:32:36 2018

[css-align] justfy-items accepts 'legacy' and drops support for 'auto'

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 <jfernandez@igalia.com>
Reviewed-by: Christian Biesinger <cbiesinger@chromium.org>
Reviewed-by: Darren Shen <shend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#535593}
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/LayoutTests/TestExpectations
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/LayoutTests/external/wpt/css/css-align/content-distribution/place-content-shorthand-004.html
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/LayoutTests/external/wpt/css/css-align/default-alignment/parse-justify-items-002.html
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/LayoutTests/external/wpt/css/css-align/default-alignment/place-items-shorthand-004.html
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/LayoutTests/fast/alignment/parse-alignment-of-root-elements.html
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/LayoutTests/fast/alignment/parse-justify-items.html
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/LayoutTests/fast/alignment/parse-place-items.html
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/Source/core/css/CSSPrimitiveValueMappings.h
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/Source/core/css/CSSProperties.json5
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/Source/core/css/properties/CSSParsingUtils.cpp
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/Source/core/css/properties/CSSParsingUtils.h
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/Source/core/css/properties/ComputedStyleUtils.cpp
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/Source/core/css/properties/longhands/JustifyItemsCustom.cpp
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/Source/core/css/properties/shorthands/PlaceItemsCustom.cpp
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/Source/core/css/properties/shorthands/PlaceSelfCustom.cpp
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/Source/core/layout/LayoutFlexibleBox.cpp
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/Source/core/layout/LayoutGrid.cpp
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/Source/core/style/ComputedStyle.cpp
[modify] https://crrev.com/464de2c5b1f00abced98a1a705889046859f5948/third_party/WebKit/Source/core/style/ComputedStyleConstants.h

This issue should be FIXED now.