Have we shipped support? If so, should we have a Deprecate and Remove?

I this case, no, we haven't shipped support for the 'baseline' value for the justify-content CSS property. 

Actually, even that the CSS syntax allows it, we haven't shipped support for 'baseline' for the align-content property either. We still have bug 	#764235 to implement such support. 

Should we also parse as invalid the 'baseline' value for align-content as well ? I had in mind to work on that anytime soon, but maybe we want to parse it as invalid meanwhile.

Firefox has a similar bug:

https://bugzilla.mozilla.org/show_bug.cgi?id=1430817

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/948b8dee181da1bd431f91229f05e73e3b423490

commit 948b8dee181da1bd431f91229f05e73e3b423490
Author: Javier Fernandez <jfernandez@igalia.com>
Date: Mon Jan 29 11:56:58 2018

[css-align] justify-content doesn't allow <baseline-position> values

The CSS WG has resolved that it doesn't make sense to define Baseline
Content-Alignment in the inline/main axis.

https://github.com/w3c/csswg-drafts/issues/1184

The spec has been updated so that <baseline-postion> is not valid for
the 'justify-content' property's syntax. This CL updates our parsing
logic to match the new spec, including the parsing logic of the
place-content shorthand.

Additionally, this CL updates the computed value of the
<baseline-position> values to match other browsers.

We don't implement support for <baseline-position> values in the
Content Distribution properties (align-content and justify-content),
so I don't expect this change to break content of sites using the CSS
Box Alignment feature.

Bug:  802248 ,  803275 
Change-Id: I0d3b1b7e7dd28552ee7e131bfe09ef7198565283
Reviewed-on: https://chromium-review.googlesource.com/882362
Reviewed-by: Darren Shen <shend@chromium.org>
Commit-Queue: Javier Fernandez <jfernandez@igalia.com>
Cr-Commit-Position: refs/heads/master@{#532400}
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/TestExpectations
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/content-distribution/parse-align-content-001.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/content-distribution/parse-align-content-003.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/content-distribution/parse-justify-content-001.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/content-distribution/parse-justify-content-003.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/content-distribution/parse-justify-content-004.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/content-distribution/place-content-shorthand-001.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/content-distribution/place-content-shorthand-002.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/content-distribution/place-content-shorthand-004.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/content-distribution/place-content-shorthand-006.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/default-alignment/parse-align-items-001.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/default-alignment/parse-align-items-003.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/default-alignment/parse-justify-items-001.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/default-alignment/parse-justify-items-003.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/default-alignment/place-items-shorthand-001.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/default-alignment/place-items-shorthand-002.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/default-alignment/place-items-shorthand-004.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/default-alignment/place-items-shorthand-006.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/resources/alignment-parsing-utils.js
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/self-alignment/parse-align-self-001.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/self-alignment/parse-align-self-003.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/self-alignment/parse-justify-self-001.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/self-alignment/parse-justify-self-003.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/self-alignment/place-self-shorthand-001.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/self-alignment/place-self-shorthand-002.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/self-alignment/place-self-shorthand-004.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/external/wpt/css/css-align/self-alignment/place-self-shorthand-006.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/fast/alignment/parse-align-content.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/fast/alignment/parse-justify-content.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/LayoutTests/fast/alignment/parse-place-content.html
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/Source/core/css/properties/CSSParsingUtils.cpp
[modify] https://crrev.com/948b8dee181da1bd431f91229f05e73e3b423490/third_party/WebKit/Source/core/css/properties/longhands/JustifyContentCustom.cpp

This issue should be FIXED now.