Stop converting widestring -> c_str -> widestring in several places.

fpdfsdk/pdfwindow/PWL_ListBox.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 FPDFSDK_PDFWINDOW_PWL_LISTBOX_H_
 #define FPDFSDK_PDFWINDOW_PWL_LISTBOX_H_
 
 #include "fpdfsdk/fxedit/include/fx_edit.h"
@@ skipping 57 matching lines @@
                 intptr_t lParam = 0) override;
   void RePosChildWnd() override;
   CFX_FloatRect GetFocusRect() const override;
   void SetFontSize(FX_FLOAT fFontSize) override;
   FX_FLOAT GetFontSize() const override;
 
   virtual CFX_WideString GetText() const;
 
   void OnNotifySelChanged(FX_BOOL bKeyDown, FX_BOOL& bExit, uint32_t nFlag);
 
-  void AddString(const FX_WCHAR* str);
+  void AddString(const CFX_WideString& str);
   void SetTopVisibleIndex(int32_t nItemIndex);
   void ScrollToListItem(int32_t nItemIndex);
   void ResetContent();
   void Reset();
   void Select(int32_t nItemIndex);
   void SetCaret(int32_t nItemIndex);
   void SetHoverSel(FX_BOOL bHoverSel);
 
   int32_t GetCount() const;
   FX_BOOL IsMultipleSel() const;
@@ skipping 18 matching lines @@
   IPWL_Filler_Notify* m_pFillerNotify;
 
  public:
   void AttachFFLData(void* pData) { m_pFormFiller = pData; }
 
  private:
   void* m_pFormFiller;
 };
 
 #endif  // FPDFSDK_PDFWINDOW_PWL_LISTBOX_H_