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

Source/core/editing/VisiblePosition.cpp

Index: Source/core/editing/VisiblePosition.cpp
diff --git a/Source/core/editing/VisiblePosition.cpp b/Source/core/editing/VisiblePosition.cpp
index a0b7697fa96a6330f951c329c190ea28b4126b18..92e4490633ce67e10212a17a535366d9088b7afd 100644
--- a/Source/core/editing/VisiblePosition.cpp
+++ b/Source/core/editing/VisiblePosition.cpp
@@ -591,14 +591,14 @@ Position VisiblePosition::canonicalPosition(const Position& passedPosition)
 
     // 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;