Use cppgc::Persistent<> in RecurseRecord structure.

Avoids a warning when built with blink-gc plugin, but the current
code is fine since we don't mark with a live stack.

Bug: pdfium:1672
Change-Id: I13a5ec57be2c0b43a9872399cf524af7ced3a3b5
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/79150
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
diff --git a/xfa/fxfa/parser/cxfa_document.cpp b/xfa/fxfa/parser/cxfa_document.cpp
index 0fc6532..f00c752 100644
--- a/xfa/fxfa/parser/cxfa_document.cpp
+++ b/xfa/fxfa/parser/cxfa_document.cpp
@@ -53,8 +53,8 @@
 const wchar_t kTemplateNS[] = L"http://www.xfa.org/schema/xfa-template/";
 
 struct RecurseRecord {
-  CXFA_Node* pTemplateChild;
-  CXFA_Node* pDataChild;
+  cppgc::Persistent<CXFA_Node> pTemplateChild;
+  cppgc::Persistent<CXFA_Node> pDataChild;
 };
 
 class CXFA_TraverseStrategy_DDGroup {