Add mutable form of CPDF_Page::GetPageAttr()

Then force const form to return const objects only.

Change-Id: I677141e66753a47c268fd0704ac61fc5627ad904
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/94610
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

core/fpdfapi/page/cpdf_page.cpp

diff --git a/core/fpdfapi/page/cpdf_page.cpp b/core/fpdfapi/page/cpdf_page.cpp
index 5aad0f1..79c411e 100644
--- a/core/fpdfapi/page/cpdf_page.cpp
+++ b/core/fpdfapi/page/cpdf_page.cpp
@@ -28,7 +28,8 @@
   // Cannot initialize |m_pResources| and |m_pPageResources| via the
   // CPDF_PageObjectHolder ctor because GetPageAttr() requires
   // CPDF_PageObjectHolder to finish initializing first.
-  CPDF_Object* pPageAttr = GetPageAttr(pdfium::page_object::kResources);
+  RetainPtr<CPDF_Object> pPageAttr =
+      GetMutablePageAttr(pdfium::page_object::kResources);
   m_pResources.Reset(pPageAttr ? pPageAttr->GetDict() : nullptr);
   m_pPageResources = m_pResources;
 
@@ -74,7 +75,11 @@
   ContinueParse(nullptr);
 }
 
-CPDF_Object* CPDF_Page::GetPageAttr(const ByteString& name) const {
+RetainPtr<CPDF_Object> CPDF_Page::GetMutablePageAttr(const ByteString& name) {
+  return pdfium::WrapRetain(const_cast<CPDF_Object*>(GetPageAttr(name)));
+}
+
+const CPDF_Object* CPDF_Page::GetPageAttr(const ByteString& name) const {
   std::set<CPDF_Dictionary*> visited;
   CPDF_Dictionary* pPageDict = GetDict();
   while (pPageDict && !pdfium::Contains(visited, pPageDict)) {
@@ -90,7 +95,7 @@
 
 CFX_FloatRect CPDF_Page::GetBox(const ByteString& name) const {
   CFX_FloatRect box;
-  CPDF_Array* pBox = ToArray(GetPageAttr(name));
+  const CPDF_Array* pBox = ToArray(GetPageAttr(name));
   if (pBox) {
     box = pBox->GetRect();
     box.Normalize();
@@ -172,7 +177,7 @@
 }
 
 int CPDF_Page::GetPageRotation() const {
-  CPDF_Object* pRotate = GetPageAttr(pdfium::page_object::kRotate);
+  const CPDF_Object* pRotate = GetPageAttr(pdfium::page_object::kRotate);
   int rotate = pRotate ? (pRotate->GetInteger() / 90) % 4 : 0;
   return (rotate < 0) ? (rotate + 4) : rotate;
 }

core/fpdfapi/page/cpdf_page.h

diff --git a/core/fpdfapi/page/cpdf_page.h b/core/fpdfapi/page/cpdf_page.h
index d2ff1ac..546b106 100644
--- a/core/fpdfapi/page/cpdf_page.h
+++ b/core/fpdfapi/page/cpdf_page.h
@@ -101,7 +101,8 @@
   CPDF_Page(CPDF_Document* pDocument, CPDF_Dictionary* pPageDict);
   ~CPDF_Page() override;
 
-  CPDF_Object* GetPageAttr(const ByteString& name) const;
+  RetainPtr<CPDF_Object> GetMutablePageAttr(const ByteString& name);
+  const CPDF_Object* GetPageAttr(const ByteString& name) const;
   CFX_FloatRect GetBox(const ByteString& name) const;
 
   CFX_SizeF m_PageSize;