Split off CPDF_Document into its own .cpp/.h files.

core/src/fpdfdoc/doc_formfield.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 "core/include/fpdfapi/cpdf_document.h"
 #include "core/include/fpdfdoc/fpdf_doc.h"
 #include "core/src/fpdfdoc/doc_utils.h"
 
 FX_BOOL PDF_FormField_IsUnison(CPDF_FormField* pField) {
   FX_BOOL bUnison = FALSE;
   if (pField->GetType() == CPDF_FormField::CheckBox) {
     bUnison = TRUE;
   } else {
     FX_DWORD dwFlags = pField->GetFieldFlags();
     bUnison = ((dwFlags & 0x2000000) != 0);
@@ skipping 1065 matching lines @@
     pFontDict = m_pForm->m_pFormDict->GetDictBy("DR")
                     ->GetDictBy("Font")
                     ->GetDictBy(font_name);
 
   if (!pFontDict) {
     return;
   }
   m_pFont = m_pForm->m_pDocument->LoadFont(pFontDict);
   m_FontSize = FX_atof(syntax.GetWord());
 }