Change IFWL_Widget to store a single delegate.

xfa/fwl/core/ifwl_combobox.cpp

Index: xfa/fwl/core/ifwl_combobox.cpp
diff --git a/xfa/fwl/core/ifwl_combobox.cpp b/xfa/fwl/core/ifwl_combobox.cpp
index 28a5977425a3c588673228bf10ef3eed2690ad17..3680bdfb79e702468c3e2d479ce2991d7ae6f8a4 100644
--- a/xfa/fwl/core/ifwl_combobox.cpp
+++ b/xfa/fwl/core/ifwl_combobox.cpp
@@ -465,7 +465,7 @@ void IFWL_ComboBox::ShowDropList(FX_BOOL bActivate) {
   if (!m_pForm) {
     InitProxyForm();
   }
-  m_pListProxyDelegate->Reset();
+  static_cast<CFWL_ComboProxyImpDelegate*>(m_pForm->GetDelegate())->Reset();
   if (bActivate) {
     m_pListBox->ChangeSelected(m_iCurSel);
     ReSetListItemAlignment();
@@ -701,8 +701,8 @@ void IFWL_ComboBox::InitProxyForm() {
 
   m_pForm = new IFWL_FormProxy(m_pOwnerApp, propForm, m_pListBox.get());
   m_pListBox->SetParent(m_pForm);
-  m_pListProxyDelegate = new CFWL_ComboProxyImpDelegate(m_pForm, this);
-  m_pForm->SetCurrentDelegate(m_pListProxyDelegate);
+  m_pForm->SetDelegate(
+      pdfium::MakeUnique<CFWL_ComboProxyImpDelegate>(m_pForm, this));
 }
 
 void IFWL_ComboBox::DisForm_InitComboList() {
@@ -1141,7 +1141,7 @@ void CFWL_ComboBoxImpDelegate::DoSubCtrlKey(CFWL_MsgKey* pMsg) {
   }
   FX_BOOL bDropDown = m_pOwner->IsDropDownStyle();
   if (bDropDown)
-    m_pOwner->m_pEdit->GetCurrentDelegate()->OnProcessMessage(pMsg);
+    m_pOwner->m_pEdit->GetDelegate()->OnProcessMessage(pMsg);
 }
 
 void CFWL_ComboBoxImpDelegate::DisForm_OnProcessMessage(
@@ -1190,8 +1190,7 @@ void CFWL_ComboBoxImpDelegate::DisForm_OnProcessMessage(
                            pKey->m_dwKeyCode == FWL_VKEY_Return ||
                            pKey->m_dwKeyCode == FWL_VKEY_Escape;
         if (bListKey) {
-          m_pOwner->m_pListBox->GetCurrentDelegate()->OnProcessMessage(
-              pMessage);
+          m_pOwner->m_pListBox->GetDelegate()->OnProcessMessage(pMessage);
           break;
         }
       }
@@ -1231,7 +1230,7 @@ void CFWL_ComboBoxImpDelegate::DisForm_OnFocusChanged(CFWL_Message* pMsg,
       CFWL_MsgSetFocus msg;
       msg.m_pDstTarget = m_pOwner->m_pEdit.get();
       msg.m_pSrcTarget = nullptr;
-      m_pOwner->m_pEdit->GetCurrentDelegate()->OnProcessMessage(&msg);
+      m_pOwner->m_pEdit->GetDelegate()->OnProcessMessage(&msg);
     }
   } else {
     m_pOwner->m_pProperties->m_dwStates &= ~FWL_WGTSTATE_Focused;
@@ -1239,7 +1238,7 @@ void CFWL_ComboBoxImpDelegate::DisForm_OnFocusChanged(CFWL_Message* pMsg,
     CFWL_MsgKillFocus msg;
     msg.m_pDstTarget = nullptr;
     msg.m_pSrcTarget = m_pOwner->m_pEdit.get();
-    m_pOwner->m_pEdit->GetCurrentDelegate()->OnProcessMessage(&msg);
+    m_pOwner->m_pEdit->GetDelegate()->OnProcessMessage(&msg);
   }
 }
 
@@ -1283,7 +1282,7 @@ void CFWL_ComboBoxImpDelegate::DisForm_OnKey(CFWL_MsgKey* pMsg) {
     return;
   }
   if (m_pOwner->m_pEdit)
-    m_pOwner->m_pEdit->GetCurrentDelegate()->OnProcessMessage(pMsg);
+    m_pOwner->m_pEdit->GetDelegate()->OnProcessMessage(pMsg);
 }
 
 CFWL_ComboProxyImpDelegate::CFWL_ComboProxyImpDelegate(IFWL_Form* pForm,