[web-animations] implement correct additivity support for the filter …

…property

https://bugs.webkit.org/show_bug.cgi?id=248225

Reviewed by Tim Nguyen.

When blending with additivity, simply concatenate the two filter lists.

* LayoutTests/imported/w3c/web-platform-tests/web-animations/animation-model/animation-types/addition-per-property-001-expected.txt:
* Source/WebCore/animation/CSSPropertyAnimation.cpp:
(WebCore::blendFilterOperations):

Canonical link: https://commits.webkit.org/256955@main

LayoutTests/imported/w3c/web-platform-tests/web-animations/animation-model/animation-types/addition-per-property-001-expected.txt

@@ -197,8 +197,8 @@ PASS fill-rule (type: discrete) has testAddition function
 PASS fill-rule: "nonzero" onto "evenodd"
 PASS fill-rule: "evenodd" onto "nonzero"
 PASS filter (type: filterList) has testAddition function
-FAIL filter: blur on blur assert_equals: The value should be blur(10px) blur(20px) at 0ms expected "blur(10px) blur(20px)" but got "blur(30px)"
-FAIL filter: different filter functions assert_equals: The value should be blur(10px) brightness(0.8) at 0ms expected "blur(10px) brightness(0.8)" but got "brightness(0.8)"
+PASS filter: blur on blur
+PASS filter: different filter functions
 PASS flex-basis (type: lengthPercentageOrCalc) has testAddition function
 PASS flex-basis: length
 PASS flex-basis: length of rem

Source/WebCore/animation/CSSPropertyAnimation.cpp

@@ -330,6 +330,14 @@ static inline RefPtr<FilterOperation> blendFunc(FilterOperation* from, FilterOpe
 
 static inline FilterOperations blendFilterOperations(const FilterOperations& from, const FilterOperations& to, const CSSPropertyBlendingContext& context)
 {
+    if (context.compositeOperation == CompositeOperation::Add) {
+        ASSERT(context.progress == 1.0);
+        FilterOperations resultOperations;
+        resultOperations.operations().appendVector(from.operations());
+        resultOperations.operations().appendVector(to.operations());
+        return resultOperations;
+    }
+
     FilterOperations result;
     size_t fromSize = from.operations().size();
     size_t toSize = to.operations().size();