[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..da671c46711ea47f225fc47076f20f7ffbc2f2de 100644
--- a/src/global-handles.h
+++ b/src/global-handles.h
@@ -113,6 +113,12 @@ enum WeaknessType {
 
 class GlobalHandles {
  public:
+  enum IterationMode {
+    HANDLE_PHANTOM_NODES_VISIT_OTHERS,
+    VISIT_OTHERS,
+    HANDLE_PHANTOM_NODES
+  };
+
   ~GlobalHandles();
 
   // Creates a new global handle that is alive until Destroy is called.
@@ -227,6 +233,7 @@ class GlobalHandles {
 
   // Iterates over weak independent or unmodified handles.
   // See the note above.
+  template <IterationMode mode>
   void IterateNewSpaceWeakUnmodifiedRoots(ObjectVisitor* v);
 
   // Identify unmodified objects that are in weak state and marks them
@@ -290,7 +297,7 @@ class GlobalHandles {
 #ifdef DEBUG
   void PrintStats();
   void Print();
-#endif
+#endif  // DEBUG
 
  private:
   explicit GlobalHandles(Isolate* isolate);