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

fpdfsdk/pdfwindow/PWL_ListBox.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 "fpdfsdk/pdfwindow/PWL_ListBox.h"
 
 #include "fpdfsdk/fxedit/include/fxet_edit.h"
 #include "fpdfsdk/fxedit/include/fxet_list.h"
@@ skipping 348 matching lines @@
 CFX_FloatRect CPWL_ListBox::GetFocusRect() const {
   if (m_pList->IsMultipleSel()) {
     CFX_FloatRect rcCaret = m_pList->GetItemRect(m_pList->GetCaret());
     rcCaret.Intersect(GetClientRect());
     return rcCaret;
   }
 
   return CPWL_Wnd::GetFocusRect();
 }
 
-void CPWL_ListBox::AddString(const FX_WCHAR* str) {
+void CPWL_ListBox::AddString(const CFX_WideString& str) {
   m_pList->AddString(str);
 }
 
 CFX_WideString CPWL_ListBox::GetText() const {
   return m_pList->GetText();
 }
 
 void CPWL_ListBox::SetFontSize(FX_FLOAT fFontSize) {
   m_pList->SetFontSize(fFontSize);
 }
@@ skipping 73 matching lines @@
                                    uint32_t nFlag) {
   if (zDelta < 0)
     m_pList->OnVK_DOWN(IsSHIFTpressed(nFlag), IsCTRLpressed(nFlag));
   else
     m_pList->OnVK_UP(IsSHIFTpressed(nFlag), IsCTRLpressed(nFlag));
 
   FX_BOOL bExit = FALSE;
   OnNotifySelChanged(FALSE, bExit, nFlag);
   return TRUE;
 }