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

core/src/fpdfapi/fpdf_page/fpdf_page_parser.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/src/fpdfapi/fpdf_page/pageint.h"
 
+#include "core/include/fpdfapi/cpdf_document.h"
 #include "core/include/fpdfapi/fpdf_module.h"
 #include "core/include/fpdfapi/fpdf_page.h"
 #include "core/include/fpdfapi/fpdf_serial.h"
 
 namespace {
 
 const char kPathOperatorSubpath = 'm';
 const char kPathOperatorLine = 'l';
 const char kPathOperatorCubicBezier1 = 'c';
 const char kPathOperatorCubicBezier2 = 'v';
@@ skipping 1782 matching lines @@
         } else {
           PDF_ReplaceAbbr(pElement);
         }
       }
       break;
     }
     default:
       break;
   }
 }