Introduce class RelocatablePosition

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

Index: third_party/WebKit/Source/core/editing/RelocatablePosition.h
diff --git a/third_party/WebKit/Source/core/editing/RelocatablePosition.h b/third_party/WebKit/Source/core/editing/RelocatablePosition.h
new file mode 100644
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+++ b/third_party/WebKit/Source/core/editing/RelocatablePosition.h
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+// 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/CoreExport.h"
+#include "core/dom/Range.h"
+
+namespace blink {
+
+// |RelocatablePosition| is a helper class for keeping track of a |Position| in
+// a document upon DOM tree changes even if the given |Position|'s original
+// 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 CORE_EXPORT RelocatablePosition final {
+    STACK_ALLOCATED();
+public:
+    explicit RelocatablePosition(const Position&);
+    ~RelocatablePosition();
+
+    Position position() const;
+
+private:
+    const Member<Range> m_range;
+
+    DISALLOW_COPY_AND_ASSIGN(RelocatablePosition);
+};
+
+} // namespace blink
+
+#endif // RelocatablePosition_h