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

core/src/fpdfdoc/doc_form.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"
 #include "third_party/base/stl_util.h"
 
 namespace {
 
 const int nMaxRecursion = 32;
 
 const struct SupportFieldEncoding {
   const FX_CHAR* m_name;
@@ skipping 1174 matching lines @@
     FDF_ImportField(pField, L"", bNotify);
   }
   if (bNotify && m_pFormNotify) {
     m_pFormNotify->AfterFormImportData(this);
   }
   return TRUE;
 }
 void CPDF_InterForm::SetFormNotify(const CPDF_FormNotify* pNotify) {
   m_pFormNotify = (CPDF_FormNotify*)pNotify;
 }