Introduce CPDF_Document::FromFPDFDocument().

core/src/fpdfapi/fpdf_parser/fpdf_parser_document.cpp

Index: core/src/fpdfapi/fpdf_parser/fpdf_parser_document.cpp
diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_document.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_document.cpp
index 5b78013694f9c87853c19a0406b1381a486593d8..b93cadd2666ee9240074ff6101360b5293e052b8 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_document.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_document.cpp
@@ -7,6 +7,11 @@
 #include "../../../include/fpdfapi/fpdf_parser.h"
 #include "../../../include/fpdfapi/fpdf_module.h"
 
+// static
+CPDF_Document* CPDF_Document::FromFPDFDocument(FPDF_DOCUMENT document) {
+  return static_cast<CPDF_Document*>(document);
+}
+
 CPDF_Document::CPDF_Document(CPDF_Parser* pParser)
     : CPDF_IndirectObjects(pParser) {
   ASSERT(pParser != NULL);