[css-align] Implement the place-items shorthand

[css-align] Implement the place-items shorthand
https://bugs.webkit.org/show_bug.cgi?id=168847

Reviewed by David Hyatt.

Source/WebCore:

The CSS Box Alignment specification defines a new shorthand to set the
Content Alignment properties (align-items and justify-items) at the
same time.

This patch provides the implementation of the CSS parsing logic and the
required regression tests. For the time being, as it happens with the
rest of the new alignment properties, the new parsing logic is
implemented behind the CSS Grid Layout runtime flag.

Test: css3/parse-place-items.html

* css/CSSComputedStyleDeclaration.cpp:
(WebCore::ComputedStyleExtractor::propertyValue):
* css/CSSProperties.json:
* css/StyleProperties.cpp:
(WebCore::StyleProperties::getPropertyValue):
(WebCore::StyleProperties::getAlignmentShorthandValue):
* css/StyleProperties.h:
* css/parser/CSSPropertyParser.cpp:
(WebCore::isAutoOrNormalOrStretch):
(WebCore::consumeSelfPositionOverflowPosition):
(WebCore::consumeSimplifiedItemPosition):
(WebCore::CSSPropertyParser::consumePlaceItemsShorthand):
* css/parser/CSSPropertyParser.h:

LayoutTests:

Regression tests for the new place-content alignment shorthand.

* css3/parse-place-items.html: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@214966 268f45cc-cd09-0410-ab3c-d52691b4dbfc