Implement ShadowRoot.delegatesFocus 4/4 (match CSS :focus for shadow host)

Source/core/dom/Node.h

Index: Source/core/dom/Node.h
diff --git a/Source/core/dom/Node.h b/Source/core/dom/Node.h
index 7e6bc65f550156a0dba0a749d03d767fd02aa7d8..5f7b375f03f26e2bf85a8884d98862b8da8ee200 100644
--- a/Source/core/dom/Node.h
+++ b/Source/core/dom/Node.h
@@ -360,6 +360,10 @@ public:
     bool active() const { return isUserActionElement() && isUserActionElementActive(); }
     bool inActiveChain() const { return isUserActionElement() && isUserActionElementInActiveChain(); }
     bool hovered() const { return isUserActionElement() && isUserActionElementHovered(); }
+    // Note: As a shadow host whose root with delegatesFocus=false may become focused state when
+    // an inner element gets focused, in that case more than one elements in a document can return
+    // true for |focused()|.  Use Element::isFocusedElementInDocument() or Document::focusedElement()
+    // to check which element is exactly focused.
     bool focused() const { return isUserActionElement() && isUserActionElementFocused(); }
 
     bool needsAttach() const { return styleChangeType() == NeedsReattachStyleChange; }