Add missing operators for CFX_WideString

core/include/fxcrt/fx_string.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_STRING_H_
 #define _FX_STRING_H_
 
+#include <algorithm>
+
 #include "fx_memory.h"
 
 class CFX_ByteStringC;
 class CFX_ByteString;
 class CFX_WideStringC;
 class CFX_WideString;
 struct CFX_CharMap;
 class CFX_BinaryBuf;
 typedef int FX_STRSIZE;
 class CFX_ByteStringL;
@@ skipping 675 matching lines @@
     const CFX_WideString&       operator =(const CFX_WideStringC& stringSrc);
 
     const CFX_WideString&       operator += (FX_LPCWSTR str);
 
     const CFX_WideString&       operator += (FX_WCHAR ch);
 
     const CFX_WideString&       operator += (const CFX_WideString& str);
 
     const CFX_WideString&       operator += (const CFX_WideStringC& str);
 
+    bool operator< (const CFX_WideString& str) const {
+        int result = wmemcmp(c_str(), str.c_str(), std::min(GetLength(), str.GetLength()));
+        return result < 0 || (result == 0 && GetLength() < str.GetLength());
+    }
+
     FX_WCHAR                            GetAt(FX_STRSIZE nIndex) const
     {
         return m_pData ? m_pData->m_String[nIndex] : 0;
     }
 
     FX_WCHAR                            operator[](FX_STRSIZE nIndex) const
     {
         return m_pData ? m_pData->m_String[nIndex] : 0;
     }
 
@@ skipping 152 matching lines @@
 CFX_ByteString  FX_UTF8Encode(FX_LPCWSTR pwsStr, FX_STRSIZE len);
 inline CFX_ByteString   FX_UTF8Encode(FX_WSTR wsStr)
 {
     return FX_UTF8Encode(wsStr.GetPtr(), wsStr.GetLength());
 }
 inline CFX_ByteString   FX_UTF8Encode(const CFX_WideString &wsStr)
 {
     return FX_UTF8Encode(wsStr.c_str(), wsStr.GetLength());
 }
 #endif