Use new is*Element() helper functions more in editing code

Source/core/editing/VisiblePosition.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Portions Copyright (c) 2011 Motorola Mobility, 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
@@ skipping 573 matching lines @@
 
     // When neither upstream or downstream gets us to a candidate (upstream/downstream won't leave
     // blocks or enter new ones), we search forward and backward until we find one.
     Position next = canonicalizeCandidate(nextCandidate(position));
     Position prev = canonicalizeCandidate(previousCandidate(position));
     Node* nextNode = next.deprecatedNode();
     Node* prevNode = prev.deprecatedNode();
 
     // The new position must be in the same editable element. Enforce that first.
     // Unless the descent is from a non-editable html element to an editable body.
-    if (node && node->hasTagName(htmlTag) && !node->rendererIsEditable() && node->document().body() && node->document().body()->rendererIsEditable())
+    if (isHTMLHtmlElement(node) && !node->rendererIsEditable() && node->document().body() && node->document().body()->rendererIsEditable())
         return next.isNotNull() ? next : prev;
 
     Node* editingRoot = editableRootForPosition(position);
 
     // If the html element is editable, descending into its body will look like a descent
     // from non-editable to editable content since rootEditableElement() always stops at the body.
-    if ((editingRoot && editingRoot->hasTagName(htmlTag)) || position.deprecatedNode()->isDocumentNode())
+    if (isHTMLHtmlElement(editingRoot) || position.deprecatedNode()->isDocumentNode())
         return next.isNotNull() ? next : prev;
 
     bool prevIsInSameEditableElement = prevNode && editableRootForPosition(prev) == editingRoot;
     bool nextIsInSameEditableElement = nextNode && editableRootForPosition(next) == editingRoot;
     if (prevIsInSameEditableElement && !nextIsInSameEditableElement)
         return prev;
 
     if (nextIsInSameEditableElement && !prevIsInSameEditableElement)
         return next;
 
@@ skipping 187 matching lines @@
     if (vpos)
         vpos->showTreeForThis();
 }
 
 void showTree(const WebCore::VisiblePosition& vpos)
 {
     vpos.showTreeForThis();
 }
 
 #endif