Fix IWYU in fxcrt headers.

core/include/fxcrt/fx_ext.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 _FXCRT_EXTENSION_
 #define _FXCRT_EXTENSION_
-#ifndef _FX_BASIC_H_
+
+#include "fx_arb.h"
 #include "fx_basic.h"
-#endif
-#ifndef _FXCRT_COORDINATES_
 #include "fx_coordinates.h"
-#endif
-#ifndef _FX_XML_H_
+#include "fx_ucd.h"
 #include "fx_xml.h"
-#endif
-#ifndef _FX_UNICODE_
-#include "fx_ucd.h"
-#endif
-#ifndef _FX_ARABIC_
-#include "fx_arb.h"
-#endif
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-
 FX_FLOAT                FXSYS_tan(FX_FLOAT a);
 FX_FLOAT                FXSYS_logb(FX_FLOAT b, FX_FLOAT x);
 FX_FLOAT                FXSYS_strtof(FX_LPCSTR pcsStr, FX_INT32 iLength = -1, FX_INT32 *pUsedLen = NULL);
 FX_FLOAT                FXSYS_wcstof(FX_LPCWSTR pwsStr, FX_INT32 iLength = -1, FX_INT32 *pUsedLen = NULL);
 FX_LPWSTR               FXSYS_wcsncpy(FX_LPWSTR dstStr, FX_LPCWSTR srcStr, size_t count);
 FX_INT32                FXSYS_wcsnicmp(FX_LPCWSTR s1, FX_LPCWSTR s2, size_t count);
 FX_INT32                FXSYS_strnicmp(FX_LPCSTR s1, FX_LPCSTR s2, size_t count);
+
 inline FX_BOOL  FXSYS_islower(FX_INT32 ch)
 {
     return ch >= 'a' && ch <= 'z';
 }
 inline FX_BOOL  FXSYS_isupper(FX_INT32 ch)
 {
     return ch >= 'A' && ch <= 'Z';
 }
 inline FX_INT32 FXSYS_tolower(FX_INT32 ch)
 {
     return ch < 'A' || ch > 'Z' ? ch : (ch + 0x20);
 }
 inline FX_INT32 FXSYS_toupper(FX_INT32 ch)
 {
     return ch < 'a' || ch > 'z' ? ch : (ch - 0x20);
 }
 
-
-
 FX_DWORD        FX_HashCode_String_GetA(FX_LPCSTR pStr, FX_INT32 iLength, FX_BOOL bIgnoreCase = FALSE);
 FX_DWORD        FX_HashCode_String_GetW(FX_LPCWSTR pStr, FX_INT32 iLength, FX_BOOL bIgnoreCase = FALSE);
 
 #ifdef __cplusplus
 }
 #endif
 #ifdef __cplusplus
 extern "C" {
 #endif
 
@@ skipping 29 matching lines @@
                     pArray[j + gap] = v2;
                     j -= gap;
                 }
                 pArray[j + gap] = v1;
             }
             gap >>= 1;
         }
     }
 };
 #endif