[css-grid] Use ShorthandSerializer for grid-area in CSSComputedStyleD…

…eclaration::getPropertyValue.

https://bugs.webkit.org/show_bug.cgi?id=261577
rdar://115521493

Reviewed by Tim Nguyen.

We can reuse the logic that the ShorthandSerializer provides to
correctly serialize the computed style of this property. This will
help us avoid duplicating logic to get the computed value.

* LayoutTests/imported/w3c/web-platform-tests/css/css-grid/grid-layout-properties-expected.txt:
* Source/WebCore/css/CSSComputedStyleDeclaration.cpp:
(WebCore::CSSComputedStyleDeclaration::getPropertyValue const):

Canonical link: https://commits.webkit.org/268026@main

LayoutTests/imported/w3c/web-platform-tests/css/css-grid/grid-layout-properties-expected.txt

@@ -129,16 +129,16 @@ PASS grid-row.span <custom-ident>
 PASS grid-row.span <integer> <custom-ident>
 FAIL grid-row.reset assert_equals: reset expected "auto" but got "auto / auto"
 PASS grid-area
-FAIL grid-area.initial assert_equals: initial value of grid-area should be auto expected "auto" but got "auto / auto / auto / auto"
-FAIL grid-area.auto assert_equals: auto expected "auto" but got "auto / auto / auto / auto"
+PASS grid-area.initial
+PASS grid-area.auto
 PASS grid-area.<custom-ident>
-FAIL grid-area.<integer> start assert_equals: <integer> start expected "1 / 2" but got "1 / 2 / auto / auto"
+PASS grid-area.<integer> start
 PASS grid-area.<integer>
 PASS grid-area.<integer> <ident>
 PASS grid-area.span <integer>
 PASS grid-area.span <custom-ident>
 PASS grid-area.span <integer> <custom-ident>
-FAIL grid-area.reset assert_equals: reset expected "auto" but got "auto / auto / auto / auto"
+PASS grid-area.reset
 I T
 IT
 I

Source/WebCore/css/CSSComputedStyleDeclaration.cpp

@@ -108,6 +108,7 @@ String CSSComputedStyleDeclaration::getPropertyValue(CSSPropertyID propertyID) c
 {
     auto canUseShorthandSerializerForPropertyValue = [&]() {
         switch (propertyID) {
+        case CSSPropertyGridArea:
         case CSSPropertyGridTemplate:
             return true;
         default: