Avoid unchecked casts in UA shadow DOM.

third_party/WebKit/Source/core/html/TextControlElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007 Apple Inc. All rights reserved.
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  *
  * 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 145 matching lines @@
   const AtomicString& attributeValue = fastGetAttribute(placeholderAttr);
   return attributeValue.getString().find(isNotLineBreak) == kNotFound;
 }
 
 bool TextControlElement::placeholderShouldBeVisible() const {
   return supportsPlaceholder() && isEmptyValue() && isEmptySuggestedValue() &&
          !isPlaceholderEmpty();
 }
 
 HTMLElement* TextControlElement::placeholderElement() const {
-  return toHTMLElement(
+  return toHTMLElementOrDie(
       userAgentShadowRoot()->getElementById(ShadowElementNames::placeholder()));
 }
 
 void TextControlElement::updatePlaceholderVisibility() {
   HTMLElement* placeholder = placeholderElement();
   if (!placeholder) {
     updatePlaceholderText();
     return;
   }
 
@@ skipping 716 matching lines @@
       TextDirection textDirection =
           element->directionalityIfhasDirAutoAttribute(isAuto);
       return textDirection == RTL ? "rtl" : "ltr";
     }
   }
 
   return "ltr";
 }
 
 HTMLElement* TextControlElement::innerEditorElement() const {
-  return toHTMLElement(
+  return toHTMLElementOrDie(
       userAgentShadowRoot()->getElementById(ShadowElementNames::innerEditor()));
 }
 
 static Position innerNodePosition(const Position& innerPosition) {
   DCHECK(!innerPosition.isBeforeAnchor());
   DCHECK(!innerPosition.isAfterAnchor());
   HTMLElement* element = toHTMLElement(innerPosition.anchorNode());
   DCHECK(element);
   NodeList* childNodes = element->childNodes();
   if (!childNodes->length())
@@ skipping 251 matching lines @@
 
 void TextControlElement::copyNonAttributePropertiesFromElement(
     const Element& source) {
   const TextControlElement& sourceElement =
       static_cast<const TextControlElement&>(source);
   m_lastChangeWasUserEdit = sourceElement.m_lastChangeWasUserEdit;
   HTMLFormControlElement::copyNonAttributePropertiesFromElement(source);
 }
 
 }  // namespace blink