Make CFX_WideString(const CFX_WideString&) explicit.

core/fxcrt/fx_basic_bstring.cpp

 // 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
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <cctype>
@@ skipping 802 matching lines @@
   ASSERT(nIndex < m_pData->m_nDataLength);
   ReallocBeforeWrite(m_pData->m_nDataLength);
   m_pData->m_String[nIndex] = ch;
 }
 
 CFX_WideString CFX_ByteString::UTF8Decode() const {
   CFX_UTF8Decoder decoder;
   for (FX_STRSIZE i = 0; i < GetLength(); i++) {
     decoder.Input((uint8_t)m_pData->m_String[i]);
   }
-  return decoder.GetResult();
+  return CFX_WideString(decoder.GetResult());
 }
 
 // static
 CFX_ByteString CFX_ByteString::FromUnicode(const FX_WCHAR* str,
                                            FX_STRSIZE len) {
   FX_STRSIZE str_len = len >= 0 ? len : FXSYS_wcslen(str);
   return FromUnicode(CFX_WideString(str, str_len));
 }
 
 // static
@@ skipping 142 matching lines @@
     fraction %= scale;
     scale /= 10;
   }
   return buf_size;
 }
 CFX_ByteString CFX_ByteString::FormatFloat(FX_FLOAT d, int precision) {
   FX_CHAR buf[32];
   FX_STRSIZE len = FX_ftoa(d, buf);
   return CFX_ByteString(buf, len);
 }