Implement CSSTransformValue.toMatrix

https://bugs.webkit.org/show_bug.cgi?id=246173
rdar://100868409

Reviewed by Antoine Quint.

Implement the toMatrix method of CSSTransformValue.

* LayoutTests/imported/w3c/web-platform-tests/css/css-typed-om/stylevalue-subclasses/cssTransformValue-toMatrix-expected.txt:
* Source/WebCore/css/typedom/transform/CSSTransformValue.cpp:
(WebCore::CSSTransformValue::toMatrix):

Canonical link: https://commits.webkit.org/255299@main

LayoutTests/imported/w3c/web-platform-tests/css/css-typed-om/stylevalue-subclasses/cssTransformValue-toMatrix-expected.txt

@@ -1,4 +1,4 @@
 
-FAIL CSSTransformValue.toMatrix() multiplies its component matrices assert_array_approx_equals: property 0, expected 10 +/- 0.000001, expected 10 but got 1
-FAIL CSSTransformValue.toMatrix() respects is2D changes in its components assert_array_approx_equals: property 0, expected -6 +/- 0.000001, expected -6 but got 1
+PASS CSSTransformValue.toMatrix() multiplies its component matrices
+PASS CSSTransformValue.toMatrix() respects is2D changes in its components
 

Source/WebCore/css/typedom/transform/CSSTransformValue.cpp

@@ -82,8 +82,20 @@ bool CSSTransformValue::is2D() const
 
 ExceptionOr<Ref<DOMMatrix>> CSSTransformValue::toMatrix()
 {
-    // FIXME: add correct behavior here.
-    return DOMMatrix::fromMatrix(DOMMatrixInit { });
+    auto matrix = TransformationMatrix();
+    auto is2D = DOMMatrixReadOnly::Is2D::Yes;
+
+    for (auto component : m_components) {
+        auto componentMatrixOrException = component->toMatrix();
+        if (componentMatrixOrException.hasException())
+            return componentMatrixOrException.releaseException();
+        auto componentMatrix = componentMatrixOrException.returnValue();
+        if (!componentMatrix->is2D())
+            is2D = DOMMatrixReadOnly::Is2D::No;
+        matrix.multiply(componentMatrix->transformationMatrix());
+    }
+
+    return DOMMatrix::create(WTFMove(matrix), is2D);
 }
 
 CSSTransformValue::CSSTransformValue(Vector<RefPtr<CSSTransformComponent>>&& transforms)