Make more CPDF_PageObjectHolder members protected.

Change-Id: Id31b9f6ac33971c47cdb378ff7f9ca7d33f899b9
Reviewed-on: https://pdfium-review.googlesource.com/32112
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: dsinclair <dsinclair@chromium.org>
diff --git a/fpdfsdk/fpdf_doc.cpp b/fpdfsdk/fpdf_doc.cpp
index 17cfce0..3e8f436 100644
--- a/fpdfsdk/fpdf_doc.cpp
+++ b/fpdfsdk/fpdf_doc.cpp
@@ -54,7 +54,7 @@
   if (!page)
     return nullptr;
 
-  CPDF_Document* pDoc = page->m_pDocument.Get();
+  CPDF_Document* pDoc = page->GetDocument();
   std::unique_ptr<CPDF_LinkList>* pHolder = pDoc->LinksContext();
   if (!pHolder->get())
     *pHolder = pdfium::MakeUnique<CPDF_LinkList>();