Enable selection for the composed tree

Source/core/layout/PendingSelection.cpp

Index: Source/core/layout/PendingSelection.cpp
diff --git a/Source/core/layout/PendingSelection.cpp b/Source/core/layout/PendingSelection.cpp
index 84f945064dc3ed8d69cefe5ae1ed5ef292621d13..d8dc8908045216be84afd15adf51d650ca621b5d 100644
--- a/Source/core/layout/PendingSelection.cpp
+++ b/Source/core/layout/PendingSelection.cpp
@@ -69,6 +69,8 @@ bool PendingSelection::isInDocumentAlgorithm(const Document& document) const
 
 bool PendingSelection::isInDocument(const Document& document) const
 {
+    if (RuntimeEnabledFeatures::selectionForWebComponentsEnabled())
+        return isInDocumentAlgorithm<VisibleSelection::InComposedTree>(document);
     return isInDocumentAlgorithm<VisibleSelection::InDOMTree>(document);
 }
 
@@ -102,6 +104,8 @@ VisibleSelection PendingSelection::calcVisibleSelectionAlgorithm() const
 
 VisibleSelection PendingSelection::calcVisibleSelection() const
 {
+    if (RuntimeEnabledFeatures::selectionForWebComponentsEnabled())
+        return calcVisibleSelectionAlgorithm<VisibleSelection::InComposedTree>();
     return calcVisibleSelectionAlgorithm<VisibleSelection::InDOMTree>();
 }