Use RelocatablePosition in CompositeEditCommand::moveParagraphs

third_party/WebKit/Source/core/editing/RelocatablePosition.h

+// Copyright 2016 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 RelocatablePosition_h
+#define RelocatablePosition_h
+
+#include "core/dom/Range.h"
+
+namespace blink {
+
+// |RelocatablePosition| is a helper class for keeping track of a |Position| in
+// a document upon DOM changes even if the given |Position|'s anchor node is
+// moved out of document. The class is implemented by using a temporary |Range|
+// object to keep track of the |Position|, and disposing the |Range| when out
+// of scope.
+class RelocatablePosition final {
+public:
+    RelocatablePosition();

[yosin_UTC9, 2016/07/06 06:50:30]

Do we really need default ctor?
Since, |RelocatablePosition| is disallow-copy-and-assign, default ctor isn't
needed.
Or, at least this bug.

+    explicit RelocatablePosition(const Position&);
+    ~RelocatablePosition();
+
+    Position position() const;
+
+private:
+    const Member<Range> m_range;
+
+    STACK_ALLOCATED();

[yosin_UTC9, 2016/07/06 06:50:30]

nit: It seems |STACK_ALLOCATED()| usually at top.

+    DISALLOW_COPY_AND_ASSIGN(RelocatablePosition);
+};
+
+} // namespace blink
+
+#endif // RelocatablePosition_h