Introduce "underlying types" to abstract XFA differences.

fpdfsdk/src/javascript/Field.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 "Field.h"
 
 #include "Document.h"
 #include "Icon.h"
@@ skipping 3379 matching lines @@
 
   CPDFSDK_InterForm* pInterForm =
       (CPDFSDK_InterForm*)m_pDocument->GetInterForm();
   ASSERT(pInterForm != NULL);
 
   CPDFSDK_Widget* pWidget = NULL;
   if (nCount == 1) {
     pWidget = pInterForm->GetWidget(pFormField->GetControl(0));
   } else {
     CPDFDoc_Environment* pEnv = m_pDocument->GetEnv();
-    ASSERT(pEnv);
-    CPDFXFA_Page* pPage =
-        (CPDFXFA_Page*)pEnv->FFI_GetCurrentPage(m_pDocument->GetDocument());
+    UnderlyingPageType* pPage = UnderlyingFromFPDFPage(
+        pEnv->FFI_GetCurrentPage(m_pDocument->GetUnderlyingDocument()));
     if (!pPage)
       return FALSE;
     if (CPDFSDK_PageView* pCurPageView = m_pDocument->GetPageView(pPage)) {
       for (int32_t i = 0; i < nCount; i++) {
         if (CPDFSDK_Widget* pTempWidget =
                 pInterForm->GetWidget(pFormField->GetControl(i))) {
           if (pTempWidget->GetPDFPage() == pCurPageView->GetPDFPage()) {
             pWidget = pTempWidget;
             break;
           }
@@ skipping 326 matching lines @@
 #define JS_FIELD_MINWIDTH 1
 #define JS_FIELD_MINHEIGHT 1
 
 void Field::AddField(CPDFSDK_Document* pDocument,
                      int nPageIndex,
                      int nFieldType,
                      const CFX_WideString& sName,
                      const CPDF_Rect& rcCoords) {
   // Not supported.
 }