[heap] Make the current GCCallbackFlags are part of {Heap}.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 5c825e77804ad06cd30b1f3ae3ae6b4d562bcd86..75b09df527e03e285d860b1b69e07e14fe2f63e4 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1362,8 +1362,9 @@ class Heap {
 
   // Starts incremental marking assuming incremental marking is currently
   // stopped.
-  void StartIncrementalMarking(int gc_flags,
-                               const GCCallbackFlags gc_callback_flags,
+  void StartIncrementalMarking(int gc_flags = kNoGCFlags,
+                               const GCCallbackFlags gc_callback_flags =
+                                   GCCallbackFlags::kNoGCCallbackFlags,
                                const char* reason = nullptr);
 
   // Performs incremental marking steps of step_size_in_bytes as long as
@@ -1670,8 +1671,6 @@ class Heap {
   ROOT_LIST(ROOT_ACCESSOR)
 #undef ROOT_ACCESSOR
 
-  int current_gc_flags() { return current_gc_flags_; }
-
   void set_current_gc_flags(int flags) {
     current_gc_flags_ = flags;
     DCHECK(!ShouldFinalizeIncrementalMarking() ||
@@ -2346,6 +2345,10 @@ class Heap {
   // Currently set GC flags that are respected by all GC components.
   int current_gc_flags_;
 
+  // Currently set GC callback flags that are used to pass information between
+  // the embedder and V8's GC.
+  GCCallbackFlags current_gc_callback_flags_;
+
   ExternalStringTable external_string_table_;
 
   VisitorDispatchTable<ScavengingCallback> scavenging_visitors_table_;