Remove some c_str() calls from StringCs in xfa docs.

xfa/fxfa/app/xfa_fffield.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 "xfa/fxfa/app/xfa_fffield.h"
 
 #include "xfa/fwl/basewidget/ifwl_edit.h"
 #include "xfa/fwl/core/cfwl_message.h"
@@ skipping 707 matching lines @@
           return 1;
         }
         IXFA_AppProvider* pAppProvider = GetApp()->GetAppProvider();
         if (pAppProvider) {
           CFX_WideString wsMessage;
           CFX_WideString wsWarning;
           pAppProvider->LoadString(XFA_IDS_NotModifyField, wsWarning);
           wsMessage += wsWarning;
           CFX_WideString wsTitle;
           pAppProvider->LoadString(XFA_IDS_CalcOverride, wsTitle);
-          pAppProvider->MsgBox(wsMessage.AsStringC(), wsTitle.AsStringC(),
-                               XFA_MBICON_Warning, XFA_MB_OK);
+          pAppProvider->MsgBox(wsMessage, wsTitle, XFA_MBICON_Warning,
+                               XFA_MB_OK);
         }
       }
         return 0;
       case XFA_ATTRIBUTEENUM_Warning: {
         if (version <= XFA_VERSION_204) {
           CXFA_Script script = calc.GetScript();
           if (!script) {
             return 1;
           }
           CFX_WideString wsExpression;
@@ skipping 10 matching lines @@
           CFX_WideString wsMessage;
           calc.GetMessageText(wsMessage);
           if (!wsMessage.IsEmpty()) {
             wsMessage += L"\r\n";
           }
           CFX_WideString wsWarning;
           pAppProvider->LoadString(XFA_IDS_ModifyField, wsWarning);
           wsMessage += wsWarning;
           CFX_WideString wsTitle;
           pAppProvider->LoadString(XFA_IDS_CalcOverride, wsTitle);
-          if (pAppProvider->MsgBox(wsMessage.AsStringC(), wsTitle.AsStringC(),
-                                   XFA_MBICON_Warning,
+          if (pAppProvider->MsgBox(wsMessage, wsTitle, XFA_MBICON_Warning,
                                    XFA_MB_YesNo) == XFA_IDYes) {
             pAcc->GetNode()->SetFlag(XFA_NODEFLAG_UserInteractive, false);
             return 1;
           }
         }
         return 0;
       }
       case XFA_ATTRIBUTEENUM_Ignore:
         return 0;
       case XFA_ATTRIBUTEENUM_Disabled:
@@ skipping 49 matching lines @@
       m_pDataAcc->ProcessEvent(XFA_ATTRIBUTEENUM_Click, &eParam);
       break;
     }
     default:
       break;
   }
 }
 
 void CXFA_FFField::OnDrawWidget(CFX_Graphics* pGraphics,
                                 const CFX_Matrix* pMatrix) {}