Move serializer related files in core/editing/ related files into core/editing/serializers/

Source/core/editing/TextOffset.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 TextOffset_h
-#define TextOffset_h
-
-#include "public/platform/Platform.h"
-#include "wtf/Forward.h"
-
-namespace blink {
-
-class Text;
-
-class TextOffset {
-    STACK_ALLOCATED();
-public:
-    TextOffset();
-    TextOffset(PassRefPtrWillBeRawPtr<Text>, int);
-    TextOffset(const TextOffset&);
-
-    Text* text() const { return m_text.get(); }
-    int offset() const { return m_offset; }
-
-    bool isNull() const;
-    bool isNotNull() const;
-
-private:
-    RefPtrWillBeMember<Text> m_text;
-    int m_offset;
-};
-
-} // namespace blink
-
-#endif // TextOffset_h