Use new is*Element() helper functions in DOM code

Source/core/dom/ShadowTreeStyleSheetCollection.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
@@ skipping 35 matching lines @@
 
 void ShadowTreeStyleSheetCollection::collectStyleSheets(StyleEngine* engine, StyleSheetCollection& collection)
 {
     DocumentOrderedList::iterator begin = m_styleSheetCandidateNodes.begin();
     DocumentOrderedList::iterator end = m_styleSheetCandidateNodes.end();
     for (DocumentOrderedList::iterator it = begin; it != end; ++it) {
         Node* node = *it;
         StyleSheet* sheet = 0;
         CSSStyleSheet* activeSheet = 0;
 
-        if (!node->isHTMLElement() || !node->hasTagName(styleTag))
+        if (!isHTMLStyleElement(*node))
             continue;
 
-        Element* element = toElement(node);
+        HTMLStyleElement* element = toHTMLStyleElement(node);
         const AtomicString& title = element->fastGetAttribute(titleAttr);
         bool enabledViaScript = false;
 
-        sheet = toHTMLStyleElement(node)->sheet();
+        sheet = element->sheet();
         if (sheet && !sheet->disabled() && sheet->isCSSStyleSheet())
             activeSheet = toCSSStyleSheet(sheet);
 
         // FIXME: clarify how PREFERRED or ALTERNATE works in shadow trees.
         // Should we set preferred/selected stylesheets name in shadow trees and
         // use the name in document?
         const AtomicString& rel = element->fastGetAttribute(relAttr);
         if (!enabledViaScript && sheet && !title.isEmpty()) {
             if (engine->preferredStylesheetSetName().isEmpty()) {
                 if (element->hasLocalName(styleTag) || !rel.contains("alternate")) {
@@ skipping 41 matching lines @@
         toShadowRoot(m_treeScope.rootNode()).host()->setNeedsStyleRecalc(SubtreeStyleChange);
 
     m_scopingNodesForStyleScoped.didRemoveScopingNodes();
     collection.swap(*this);
     updateUsesRemUnits();
 
     return change.requiresFullStyleRecalc;
 }
 
 }