Introduce Node::containingTreeScope(), which asserts that the node's root is a tree scope

third_party/WebKit/Source/core/dom/Element.h

Index: third_party/WebKit/Source/core/dom/Element.h
diff --git a/third_party/WebKit/Source/core/dom/Element.h b/third_party/WebKit/Source/core/dom/Element.h
index 522b8c0a5f5947bb6e8b97c1e2e838485a7d9c17..0cc727779c3f23970d0b5af2ba0efe72fe275fbf 100644
--- a/third_party/WebKit/Source/core/dom/Element.h
+++ b/third_party/WebKit/Source/core/dom/Element.h
@@ -425,6 +425,7 @@ public:
     virtual bool isKeyboardFocusable() const;
     virtual bool isMouseFocusable() const;
     bool isFocusedElementInDocument() const;
+    Element* adjustedFocusedElementInTreeScope() const;
 
     virtual void dispatchFocusEvent(Element* oldFocusedElement, WebFocusType, InputDeviceCapabilities* sourceCapabilities = nullptr);
     virtual void dispatchBlurEvent(Element* newFocusedElement, WebFocusType, InputDeviceCapabilities* sourceCapabilities = nullptr);
@@ -885,7 +886,7 @@ inline void Node::removedFrom(ContainerNode* insertionPoint)
         clearFlag(InDocumentFlag);
         insertionPoint->document().decrementNodeCount();
     }
-    if (isInShadowTree() && !treeScope().rootNode().isShadowRoot())
+    if (isInShadowTree() && !containingTreeScope().rootNode().isShadowRoot())
         clearFlag(IsInShadowTreeFlag);
     if (AXObjectCache* cache = document().existingAXObjectCache())
         cache->remove(this);