Make CFX_WideString(const CFX_WideString&) explicit.

core/fxcrt/include/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 CORE_FXCRT_INCLUDE_FX_STRING_H_
 #define CORE_FXCRT_INCLUDE_FX_STRING_H_
 
 #include <stdint.h>  // For intptr_t.
@@ skipping 232 matching lines @@
   CFX_WideString(const CFX_WideString& other) : m_pData(other.m_pData) {}
   CFX_WideString(CFX_WideString&& other) { m_pData.Swap(other.m_pData); }
 
   // Deliberately implicit to avoid calling on every string literal.
   CFX_WideString(FX_WCHAR ch);
   CFX_WideString(const FX_WCHAR* ptr)
       : CFX_WideString(ptr, ptr ? FXSYS_wcslen(ptr) : 0) {}
 
   CFX_WideString(const FX_WCHAR* ptr, FX_STRSIZE len);
 
-  // TODO(tsepez): mark constructor as explicit.
-  CFX_WideString(const CFX_WideStringC& str);
+  explicit CFX_WideString(const CFX_WideStringC& str);
   CFX_WideString(const CFX_WideStringC& str1, const CFX_WideStringC& str2);
 
   ~CFX_WideString();
 
   static CFX_WideString FromLocal(const CFX_ByteStringC& str);
   static CFX_WideString FromCodePage(const CFX_ByteStringC& str,
                                      uint16_t codepage);
 
   static CFX_WideString FromUTF8(const CFX_ByteStringC& str);
   static CFX_WideString FromUTF16LE(const unsigned short* str, FX_STRSIZE len);
@@ skipping 173 matching lines @@
 }
 
 FX_FLOAT FX_atof(const CFX_ByteStringC& str);
 inline FX_FLOAT FX_atof(const CFX_WideStringC& wsStr) {
   return FX_atof(FX_UTF8Encode(wsStr.c_str(), wsStr.GetLength()).c_str());
 }
 void FX_atonum(const CFX_ByteStringC& str, FX_BOOL& bInteger, void* pData);
 FX_STRSIZE FX_ftoa(FX_FLOAT f, FX_CHAR* buf);
 
 #endif  // CORE_FXCRT_INCLUDE_FX_STRING_H_