Fix IWYU in fxcrt headers.

core/include/fxcrt/fx_xml.h

 // Copyright 2014 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 _FX_XML_H_
 #define _FX_XML_H_
-#ifndef _FX_BASIC_H_
+
 #include "fx_basic.h"
-#endif
+
 class CXML_AttrItem : public CFX_Object
 {
 public:
     CFX_ByteString      m_QSpaceName;
     CFX_ByteString      m_AttrName;
     CFX_WideString      m_Value;
 };
 class CXML_AttrMap : public CFX_Object
 {
 public:
@@ skipping 148 matching lines @@
     CFX_ByteString                      m_QSpaceName;
     CFX_ByteString                      m_TagName;
 
     CXML_AttrMap                        m_AttrMap;
 
     CFX_PtrArray                        m_Children;
     friend class CXML_Parser;
     friend class CXML_Composer;
 };
 #endif