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

xfa/fwl/lightwidget/cfwl_combobox.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_combobox.h"
 
 #include <utility>
 
@@ skipping 230 matching lines @@
 }
 
 CFWL_ComboBox::CFWL_ComboBoxDP::~CFWL_ComboBoxDP() {}
 
 FWL_Error CFWL_ComboBox::CFWL_ComboBoxDP::GetCaption(
     IFWL_Widget* pWidget,
     CFX_WideString& wsCaption) {
   return FWL_Error::Succeeded;
 }
 
-int32_t CFWL_ComboBox::CFWL_ComboBoxDP::CountItems(IFWL_Widget* pWidget) {
+int32_t CFWL_ComboBox::CFWL_ComboBoxDP::CountItems(const IFWL_Widget* pWidget) {
   return m_ItemArray.size();
 }
 
-IFWL_ListItem* CFWL_ComboBox::CFWL_ComboBoxDP::GetItem(IFWL_Widget* pWidget,
-                                                       int32_t nIndex) {
+IFWL_ListItem* CFWL_ComboBox::CFWL_ComboBoxDP::GetItem(
+    const IFWL_Widget* pWidget,
+    int32_t nIndex) {
   if (nIndex < 0 || static_cast<size_t>(nIndex) >= m_ItemArray.size())
     return nullptr;
 
   return m_ItemArray[nIndex].get();
 }
 
 int32_t CFWL_ComboBox::CFWL_ComboBoxDP::GetItemIndex(IFWL_Widget* pWidget,
                                                      IFWL_ListItem* pItem) {
   auto it = std::find_if(
       m_ItemArray.begin(), m_ItemArray.end(),
@@ skipping 111 matching lines @@
   return FWL_Error::Succeeded;
 }
 
 FX_FLOAT CFWL_ComboBox::CFWL_ComboBoxDP::GetListHeight(IFWL_Widget* pWidget) {
   return m_fMaxListHeight;
 }
 
 CFWL_ComboBoxItem::CFWL_ComboBoxItem() : m_pDIB(nullptr), m_pData(nullptr) {}
 
 CFWL_ComboBoxItem::~CFWL_ComboBoxItem() {}