Change IFWL_Widget to store a single delegate.

xfa/fxfa/app/cxfa_fflistboxdelegate.cpp

+// Copyright 2016 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/cxfa_fflistboxdelegate.h"
+
+#include "xfa/fxfa/app/xfa_ffchoicelist.h"
+
+CXFA_FFListBoxDelegate::CXFA_FFListBoxDelegate(
+    std::unique_ptr<IFWL_WidgetDelegate> pDelegate,
+    CXFA_FFListBox* const pWidget)
+    : CXFA_FFFieldDelegate(std::move(pDelegate), pWidget) {}
+
+CXFA_FFListBoxDelegate::~CXFA_FFListBoxDelegate() {}
+
+void CXFA_FFListBoxDelegate::OnProcessMessage(CFWL_Message* pMessage) {
+  m_pDelegate->OnProcessMessage(pMessage);
+}
+
+void CXFA_FFListBoxDelegate::OnProcessEvent(CFWL_Event* pEvent) {
+  CXFA_FFFieldDelegate::OnProcessEvent(pEvent);
+  switch (pEvent->GetClassID()) {
+    case CFWL_EventType::SelectChanged: {
+      CFX_Int32Array arrSels;
+      CXFA_FFListBox* widget = static_cast<CXFA_FFListBox*>(m_pWidget);
+      widget->OnSelectChanged(widget->GetNormalWidget()->GetWidget(), arrSels);
+      break;
+    }
+    default:
+      break;
+  }
+  m_pDelegate->OnProcessEvent(pEvent);
+}
+
+void CXFA_FFListBoxDelegate::OnDrawWidget(CFX_Graphics* pGraphics,
+                                          const CFX_Matrix* pMatrix) {
+  m_pDelegate->OnDrawWidget(pGraphics, pMatrix);
+}