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

core/src/fpdfdoc/doc_metadata.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/include/fxcrt/fx_xml.h"
 
 CPDF_Metadata::CPDF_Metadata(CPDF_Document* pDoc) {
   CPDF_Dictionary* pRoot = pDoc->GetRoot();
   if (!pRoot)
     return;
 
   CPDF_Stream* pStream = pRoot->GetStreamBy("Metadata");
   if (!pStream)
     return;
 
   CPDF_StreamAcc acc;
   acc.LoadAllData(pStream, FALSE);
   m_pXmlElement.reset(CXML_Element::Parse(acc.GetData(), acc.GetSize()));
 }
 
 CPDF_Metadata::~CPDF_Metadata() {}
 
 const CXML_Element* CPDF_Metadata::GetRoot() const {
   return m_pXmlElement.get();
 }