Introduce EditingAlgorithm<Traversal> class

Source/core/editing/EditingStrategy.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef EditingStrategy_h
 #define EditingStrategy_h
 
 #include "core/dom/NodeTraversal.h"
 #include "core/dom/shadow/ComposedTreeTraversal.h"
 
 namespace blink {
 
 template <typename Strategy>
 class PositionAlgorithm;
 
 template <typename Strategy>
 class PositionIteratorAlgorithm;
 
-class EditingStrategy : public NodeTraversal {
+// Editing algorithm defined on node traversal.
+template <typename Traversal>
+class EditingAlgorithm : public Traversal {
 public:
-    using PositionType = PositionAlgorithm<EditingStrategy>;
-    using PositionIteratorType = PositionIteratorAlgorithm<EditingStrategy>;
-
     // |disconnected| is optional output parameter having true if specified
     // positions don't have common ancestor.
     static short comparePositions(Node* containerA, int offsetA, Node* containerB, int offsetB, bool* disconnected = nullptr);
+    static bool isEmptyNonEditableNodeInEditable(const Node*);
     static bool editingIgnoresContent(const Node*);
     static int lastOffsetForEditing(const Node*);
 };
 
+// DOM tree version of editing algorithm
+class EditingStrategy : public EditingAlgorithm<NodeTraversal> {
+public:
+    using PositionIteratorType = PositionIteratorAlgorithm<EditingStrategy>;
+    using PositionType = PositionAlgorithm<EditingStrategy>;
+};
+
+extern template class EditingAlgorithm<NodeTraversal>;
+
 } // namespace blink
 
 #endif // EditingStrategy_h