Move xfa/fwl/core to xfa/fwl.

xfa/fwl/core/cfwl_themebackground.h

-// Copyright 2016 PDFium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
-
-#ifndef XFA_FWL_CORE_CFWL_THEMEBACKGROUND_H_
-#define XFA_FWL_CORE_CFWL_THEMEBACKGROUND_H_
-
-#include "core/fxge/fx_dib.h"
-#include "xfa/fwl/core/cfwl_themepart.h"
-
-class CFX_DIBitmpa;
-class CFX_Graphics;
-class CFX_Path;
-
-class CFWL_ThemeBackground : public CFWL_ThemePart {
- public:
-  CFWL_ThemeBackground()
-      : m_pGraphics(nullptr), m_pImage(nullptr), m_pPath(nullptr) {}
-
-  CFX_Graphics* m_pGraphics;
-  CFX_DIBitmap* m_pImage;
-  CFX_Path* m_pPath;
-};
-
-#endif  // XFA_FWL_CORE_CFWL_THEMEBACKGROUND_H_