Merge the CFWL_*Imp classes into the IFWL_* classes.

xfa/fwl/lightwidget/cfwl_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 "xfa/fwl/lightwidget/cfwl_listbox.h"
 
 #include <memory>
 
@@ skipping 199 matching lines @@
 CFWL_ListBox::CFWL_ListBoxDP::CFWL_ListBoxDP() {}
 
 CFWL_ListBox::CFWL_ListBoxDP::~CFWL_ListBoxDP() {}
 
 FWL_Error CFWL_ListBox::CFWL_ListBoxDP::GetCaption(IFWL_Widget* pWidget,
                                                    CFX_WideString& wsCaption) {
   wsCaption = m_wsData;
   return FWL_Error::Succeeded;
 }
 
-int32_t CFWL_ListBox::CFWL_ListBoxDP::CountItems(IFWL_Widget* pWidget) {
+int32_t CFWL_ListBox::CFWL_ListBoxDP::CountItems(const IFWL_Widget* pWidget) {
   return pdfium::CollectionSize<int32_t>(m_ItemArray);
 }
 
-IFWL_ListItem* CFWL_ListBox::CFWL_ListBoxDP::GetItem(IFWL_Widget* pWidget,
+IFWL_ListItem* CFWL_ListBox::CFWL_ListBoxDP::GetItem(const IFWL_Widget* pWidget,
                                                      int32_t nIndex) {
   if (nIndex < 0 || nIndex >= CountItems(pWidget))
     return nullptr;
 
   return m_ItemArray[nIndex].get();
 }
 
 int32_t CFWL_ListBox::CFWL_ListBoxDP::GetItemIndex(IFWL_Widget* pWidget,
                                                    IFWL_ListItem* pItem) {
   auto it = std::find_if(
@@ skipping 111 matching lines @@
   m_rtItem.Reset();
   m_dwStates = 0;
   m_wsText = L"";
   m_pDIB = nullptr;
   m_pData = nullptr;
   m_dwCheckState = 0;
   m_rtCheckBox.Reset();
 }
 
 CFWL_ListItem::~CFWL_ListItem() {}