Remove CFWL_Widget::SetOuter().

The one place it is called does not change the value from what
was specified one line above during creation.

-- Make a const member as a result.

Change-Id: I61690072afc95e74f721ad2bfbda5b97d8a8ccd9
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/72652
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

xfa/fwl/cfwl_combobox.cpp

diff --git a/xfa/fwl/cfwl_combobox.cpp b/xfa/fwl/cfwl_combobox.cpp
index 707739b..b14b7dd 100644
--- a/xfa/fwl/cfwl_combobox.cpp
+++ b/xfa/fwl/cfwl_combobox.cpp
@@ -424,7 +424,6 @@
 
   m_pEdit =
       std::make_unique<CFWL_ComboEdit>(GetOwnerApp(), std::move(prop), this);
-  m_pEdit->SetOuter(this);
 }
 
 void CFWL_ComboBox::OnProcessMessage(CFWL_Message* pMessage) {

xfa/fwl/cfwl_widget.h

diff --git a/xfa/fwl/cfwl_widget.h b/xfa/fwl/cfwl_widget.h
index f6a85da..2a790de 100644
--- a/xfa/fwl/cfwl_widget.h
+++ b/xfa/fwl/cfwl_widget.h
@@ -102,7 +102,6 @@
   CFWL_WidgetMgr* GetWidgetMgr() const { return m_pWidgetMgr.Get(); }
   CFWL_Widget* GetOwner() { return m_pWidgetMgr->GetOwnerWidget(this); }
   CFWL_Widget* GetOuter() const { return m_pOuter; }
-  void SetOuter(CFWL_Widget* pOuter) { m_pOuter = pOuter; }
   CFWL_Widget* GetOutmost() const;
 
   void ModifyStyles(uint32_t dwStylesAdded, uint32_t dwStylesRemoved);
@@ -186,7 +185,7 @@
   UnownedPtr<const CFWL_App> const m_pOwnerApp;
   UnownedPtr<CFWL_WidgetMgr> const m_pWidgetMgr;
   std::unique_ptr<CFWL_WidgetProperties> m_pProperties;
-  CFWL_Widget* m_pOuter;
+  CFWL_Widget* const m_pOuter;
   AdapterIface* m_pAdapterIface = nullptr;
   UnownedPtr<IFWL_WidgetDelegate> m_pDelegate;
 };