Remove CFWL_WidgetMgr::NextTab().

It always returns nullptr after traversing the entire tree. In turn,
remove logic that could only occur following a non-null return.

Bug: pdfium:1578
Change-Id: I98abfe329e0e6221bf6771593d7bb256d7401cca
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/72650
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

xfa/fwl/cfwl_notedriver.cpp

diff --git a/xfa/fwl/cfwl_notedriver.cpp b/xfa/fwl/cfwl_notedriver.cpp
index 2503ef6..6259c3c 100644
--- a/xfa/fwl/cfwl_notedriver.cpp
+++ b/xfa/fwl/cfwl_notedriver.cpp
@@ -171,22 +171,6 @@
 #if !defined(OS_APPLE)
   if (pMsg->m_dwCmd == CFWL_MessageKey::Type::kKeyDown &&
       pMsg->m_dwKeyCode == XFA_FWL_VKEY_Tab) {
-    CFWL_WidgetMgr* pWidgetMgr = pMessageForm->GetOwnerApp()->GetWidgetMgr();
-    CFWL_Widget* pForm = GetMessageForm(pMsg->GetDstTarget());
-    CFWL_Widget* pFocus = m_pFocus.Get();
-    if (m_pFocus && pWidgetMgr->GetSystemFormWidget(m_pFocus.Get()) != pForm)
-      pFocus = nullptr;
-
-    CFWL_Widget* pNextTabStop = nullptr;
-    if (pForm) {
-      pNextTabStop = CFWL_WidgetMgr::NextTab(pForm, pFocus);
-      if (!pNextTabStop)
-        pNextTabStop = CFWL_WidgetMgr::NextTab(pForm, nullptr);
-    }
-    if (pNextTabStop == pFocus)
-      return true;
-    if (pNextTabStop)
-      SetFocus(pNextTabStop);
     return true;
   }
 #endif

xfa/fwl/cfwl_widgetmgr.cpp

diff --git a/xfa/fwl/cfwl_widgetmgr.cpp b/xfa/fwl/cfwl_widgetmgr.cpp
index bd9afd0..57fada3 100644
--- a/xfa/fwl/cfwl_widgetmgr.cpp
+++ b/xfa/fwl/cfwl_widgetmgr.cpp
@@ -20,20 +20,6 @@
 
 CFWL_WidgetMgr::~CFWL_WidgetMgr() = default;
 
-// static
-CFWL_Widget* CFWL_WidgetMgr::NextTab(CFWL_Widget* parent, CFWL_Widget* focus) {
-  CFWL_WidgetMgr* pMgr = parent->GetOwnerApp()->GetWidgetMgr();
-  CFWL_Widget* child = pMgr->GetFirstChildWidget(parent);
-  while (child) {
-    CFWL_Widget* bRet = NextTab(child, focus);
-    if (bRet)
-      return bRet;
-
-    child = pMgr->GetNextSiblingWidget(child);
-  }
-  return nullptr;
-}
-
 CFWL_Widget* CFWL_WidgetMgr::GetParentWidget(const CFWL_Widget* pWidget) const {
   Item* pItem = GetWidgetMgrItem(pWidget);
   return pItem && pItem->pParent ? pItem->pParent->pWidget : nullptr;

xfa/fwl/cfwl_widgetmgr.h

diff --git a/xfa/fwl/cfwl_widgetmgr.h b/xfa/fwl/cfwl_widgetmgr.h
index 59f5751..4562716 100644
--- a/xfa/fwl/cfwl_widgetmgr.h
+++ b/xfa/fwl/cfwl_widgetmgr.h
@@ -34,8 +34,6 @@
   explicit CFWL_WidgetMgr(AdapterIface* pAdapterNative);
   ~CFWL_WidgetMgr();
 
-  static CFWL_Widget* NextTab(CFWL_Widget* parent, CFWL_Widget* focus);
-
   void OnProcessMessageToForm(std::unique_ptr<CFWL_Message> pMessage);
   void OnDrawWidget(CFWL_Widget* pWidget,
                     CXFA_Graphics* pGraphics,