Avoid unchecked casts in UA shadow DOM.

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003-2011, 2013, 2014 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 943 matching lines @@
 inline const T& toElement(const Node& node) {
   SECURITY_DCHECK(isElementOfType<const T>(node));
   return static_cast<const T&>(node);
 }
 template <typename T>
 inline const T* toElement(const Node* node) {
   SECURITY_DCHECK(!node || isElementOfType<const T>(*node));
   return static_cast<const T*>(node);
 }
 
+template <typename T>
+inline T& toElementOrDie(Node& node) {
+  CHECK(isElementOfType<const T>(node));
+  return static_cast<T&>(node);
+}
+template <typename T>
+inline T* toElementOrDie(Node* node) {
+  CHECK(!node || isElementOfType<const T>(*node));
+  return static_cast<T*>(node);
+}
+template <typename T>
+inline const T& toElementOrDie(const Node& node) {
+  CHECK(isElementOfType<const T>(node));
+  return static_cast<const T&>(node);
+}
+template <typename T>
+inline const T* toElementOrDie(const Node* node) {
+  CHECK(!node || isElementOfType<const T>(*node));
+  return static_cast<const T*>(node);
+}
+
 inline bool isDisabledFormControl(const Node* node) {
   return node->isElementNode() && toElement(node)->isDisabledFormControl();
 }
 
 inline Element* Node::parentElement() const {
   ContainerNode* parent = parentNode();
   return parent && parent->isElementNode() ? toElement(parent) : nullptr;
 }
 
 inline bool Element::fastHasAttribute(const QualifiedName& name) const {
@@ skipping 181 matching lines @@
 #define DECLARE_ELEMENT_FACTORY_WITH_TAGNAME(T) \
   static T* create(const QualifiedName&, Document&)
 #define DEFINE_ELEMENT_FACTORY_WITH_TAGNAME(T)                     \
   T* T::create(const QualifiedName& tagName, Document& document) { \
     return new T(tagName, document);                               \
   }
 
 }  // namespace blink
 
 #endif  // Element_h