Avoid unchecked casts in UA shadow DOM.

third_party/WebKit/Source/core/html/shadow/DateTimeEditElement.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 506 matching lines @@
 DateTimeEditElement::~DateTimeEditElement() {}
 
 DEFINE_TRACE(DateTimeEditElement) {
   visitor->trace(m_fields);
   visitor->trace(m_editControlOwner);
   HTMLDivElement::trace(visitor);
 }
 
 inline Element* DateTimeEditElement::fieldsWrapperElement() const {
   DCHECK(firstChild());
-  return toElement(firstChild());
+  return toElementOrDie(firstChild());
 }
 
 void DateTimeEditElement::addField(DateTimeFieldElement* field) {
   if (m_fields.size() >= maximumNumberOfFields)
     return;
   m_fields.append(field);
   fieldsWrapperElement()->appendChild(field);
 }
 
 bool DateTimeEditElement::anyEditableFieldsHaveValues() const {
@@ skipping 311 matching lines @@
 }
 
 DateTimeFieldsState DateTimeEditElement::valueAsDateTimeFieldsState() const {
   DateTimeFieldsState dateTimeFieldsState;
   for (size_t fieldIndex = 0; fieldIndex < m_fields.size(); ++fieldIndex)
     m_fields[fieldIndex]->populateDateTimeFieldsState(dateTimeFieldsState);
   return dateTimeFieldsState;
 }
 
 }  // namespace blink