[heap] Minor MC: Add marking

src/global-handles.h

Index: src/global-handles.h
diff --git a/src/global-handles.h b/src/global-handles.h
index 50e5ed6969b0f9a8a113fb4fe62bc48335890c18..f6578f1e33bb460341f8820f7ac89b1b55e8fd47 100644
--- a/src/global-handles.h
+++ b/src/global-handles.h
@@ -113,6 +113,8 @@ enum WeaknessType {
 
 class GlobalHandles {
  public:
+  enum IterationMode { HANDLE_PHANTOM_NODES, DONT_HANDLE_PHANTOM_NODES };
+
   ~GlobalHandles();
 
   // Creates a new global handle that is alive until Destroy is called.
@@ -227,8 +229,11 @@ class GlobalHandles {
 
   // Iterates over weak independent or unmodified handles.
   // See the note above.
+  template <IterationMode mode>
   void IterateNewSpaceWeakUnmodifiedRoots(ObjectVisitor* v);
 
+  void ResetNewSpaceHandlesForTesting();
+
   // Identify unmodified objects that are in weak state and marks them
   // unmodified
   void IdentifyWeakUnmodifiedObjects(WeakSlotCallback is_unmodified);