Pass new flags to cppgc heap initialization.

Ensure the marking phase is only run when PDFium is not
actively mutating memory.

REQUIRES V8 Roll past d46c94d before landing.

Bug: chromium:1156170
Change-Id: If401c0f0ac3cf5a1fa010a892b9bc6de1e7dd025
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/76910
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Hui Yingst <nigi@chromium.org>

fxjs/gc/heap.cpp

diff --git a/fxjs/gc/heap.cpp b/fxjs/gc/heap.cpp
index 2c02752..45e3df7 100644
--- a/fxjs/gc/heap.cpp
+++ b/fxjs/gc/heap.cpp
@@ -73,8 +73,14 @@
   ++g_platform_ref_count;
   auto heap = cppgc::Heap::Create(
       std::make_shared<CFXGC_Platform>(),
-      {{}, cppgc::Heap::StackSupport::kNoConservativeStackScan, {}});
-
+      cppgc::Heap::HeapOptions{
+          {},
+          cppgc::Heap::StackSupport::kNoConservativeStackScan,
+          cppgc::Heap::MarkingType::kAtomic,
+          // TODO(tsepez): switch to incremental sweeping when the issue
+          // in https://crbug.com/1156170 is resolved.
+          cppgc::Heap::SweepingType::kAtomic,
+          {}});
   return FXGCScopedHeap(heap.release());
 }