Bug fix: toPositionInComposedTree should treat positions with shadow roots

Source/core/dom/Position.cpp

Index: Source/core/dom/Position.cpp
diff --git a/Source/core/dom/Position.cpp b/Source/core/dom/Position.cpp
index 47dd2ba12d41d1d0847a05be9004b4e8acc3a4ad..45bf6b8ff03a83fdda2489d769ee3b2a35d2e197 100644
--- a/Source/core/dom/Position.cpp
+++ b/Source/core/dom/Position.cpp
@@ -1411,11 +1411,17 @@ PositionInComposedTree toPositionInComposedTree(const Position& pos)
         ASSERT(!isActiveInsertionPoint(*anchor));
         int offset = pos.computeOffsetInContainerNode();
         Node* child = NodeTraversal::childAt(*anchor, offset);
-        if (!child)
+        if (!child) {
+            if (anchor->isShadowRoot())
+                return PositionInComposedTree(anchor->shadowHost(), PositionInComposedTree::PositionIsAfterChildren);
             return PositionInComposedTree(anchor, PositionInComposedTree::PositionIsAfterChildren);
+        }
         child->updateDistribution();
-        if (isActiveInsertionPoint(*child))
+        if (isActiveInsertionPoint(*child)) {
+            if (anchor->isShadowRoot())
+                return PositionInComposedTree(anchor->shadowHost(), offset, PositionInComposedTree::PositionIsOffsetInAnchor);
             return PositionInComposedTree(anchor, offset, PositionInComposedTree::PositionIsOffsetInAnchor);
+        }
         return PositionInComposedTree(ComposedTreeTraversal::parent(*child), ComposedTreeTraversal::index(*child), PositionInComposedTree::PositionIsOffsetInAnchor);
     }