Generate scroll/clip display item hierarchy for SPv2

Source/platform/graphics/paint/FixedPositionDisplayItem.cpp

Index: Source/platform/graphics/paint/FixedPositionDisplayItem.cpp
diff --git a/Source/platform/graphics/paint/FixedPositionDisplayItem.cpp b/Source/platform/graphics/paint/FixedPositionDisplayItem.cpp
index cf19006ebcba883f51c1053e5c7e9f6d8173f5ce..6641f08a013f5bd00457316f65e76750dd5f115f 100644
--- a/Source/platform/graphics/paint/FixedPositionDisplayItem.cpp
+++ b/Source/platform/graphics/paint/FixedPositionDisplayItem.cpp
@@ -13,12 +13,18 @@ namespace blink {
 
 void BeginFixedPositionDisplayItem::appendToWebDisplayItemList(WebDisplayItemList* list) const
 {
-    // TODO(trchen): Should implement the compositor counterpart and update transform tree algorithm.
+    // Note: This is only temporarily workaround before we implement true
+    // transform-tree-based rasterization.
+    AffineTransform transform;
+    transform.translate(m_counterScroll.width(), m_counterScroll.height());
+    list->appendTransformItem(affineTransformToSkMatrix(transform));
 }
 
 void EndFixedPositionDisplayItem::appendToWebDisplayItemList(WebDisplayItemList* list) const
 {
-    // TODO(trchen): Should implement the compositor counterpart and update transform tree algorithm.
+    // Note: This is only temporarily workaround before we implement true
+    // transform-tree-based rasterization.
+    list->appendEndTransformItem();
 }
 
 } // namespace blink