Make sure computed values for 'baseline-shift' CSS property have 'px'…

… unit for lengths

https://bugs.webkit.org/show_bug.cgi?id=249318

Reviewed by Simon Fraser.

Make sure computed values for 'baseline-shift' CSS property have 'px' unit for lengths.
This is similar to what we do for other types of CSS properties. However, this SVG CSS
property would previously only compute to 'px' when applied to a SVGElement.

* LayoutTests/imported/w3c/web-platform-tests/css/css-typed-om/the-stylepropertymap/properties/baseline-shift-expected.txt:
* Source/WebCore/css/SVGCSSComputedStyleDeclaration.cpp:
(WebCore::ComputedStyleExtractor::svgPropertyValue):

Canonical link: https://commits.webkit.org/257928@main

LayoutTests/imported/w3c/web-platform-tests/css/css-typed-om/the-stylepropertymap/properties/baseline-shift-expected.txt

@@ -11,8 +11,8 @@ PASS Can set 'baseline-shift' to a percent: -3.14%
 PASS Can set 'baseline-shift' to a percent: 3.14%
 PASS Can set 'baseline-shift' to a percent: calc(0% + 0%)
 PASS Can set 'baseline-shift' to a length: 0px
-FAIL Can set 'baseline-shift' to a length: -3.14em assert_equals: unit expected "px" but got "em"
-FAIL Can set 'baseline-shift' to a length: 3.14cm assert_equals: unit expected "px" but got "cm"
+PASS Can set 'baseline-shift' to a length: -3.14em
+PASS Can set 'baseline-shift' to a length: 3.14cm
 PASS Can set 'baseline-shift' to a length: calc(0px + 0em)
 PASS Setting 'baseline-shift' to a time: 0s throws TypeError
 PASS Setting 'baseline-shift' to a time: -3.14ms throws TypeError

Source/WebCore/css/SVGCSSComputedStyleDeclaration.cpp

@@ -154,8 +154,12 @@ RefPtr<CSSValue> ComputedStyleExtractor::svgPropertyValue(CSSPropertyID property
             return CSSPrimitiveValue::createIdentifier(CSSValueSuper);
         case BaselineShift::Sub:
             return CSSPrimitiveValue::createIdentifier(CSSValueSub);
-        case BaselineShift::Length:
-            return svgStyle.baselineShiftValue().toCSSPrimitiveValue(m_element.get());
+        case BaselineShift::Length: {
+            auto computedValue = svgStyle.baselineShiftValue().toCSSPrimitiveValue(m_element.get());
+            if (computedValue->isLength() && computedValue->primitiveType() != CSSUnitType::CSS_PX)
+                return CSSPrimitiveValue::create(computedValue->doubleValue(CSSUnitType::CSS_PX), CSSUnitType::CSS_PX);
+            return computedValue;
+        }
         }
         ASSERT_NOT_REACHED();
         return nullptr;