Add initial semi-working producers profile.

src/global-handles.h

Index: src/global-handles.h
diff --git a/src/global-handles.h b/src/global-handles.h
index 9e63ba7a9730fa146780b7dc85f2a59b355b8b17..feb95bf2a3dfe7d73ecd4d2e1e401d07c22e3e90 100644
--- a/src/global-handles.h
+++ b/src/global-handles.h
@@ -54,6 +54,8 @@ class ObjectGroup : public Malloced {
 };
 
 
+typedef void (*WeakReferenceGuest)(Object* object, void* parameter);
+
 class GlobalHandles : public AllStatic {
  public:
   // Creates a new global handle that is alive until Destroy is called.
@@ -99,6 +101,10 @@ class GlobalHandles : public AllStatic {
   // Iterates over all weak roots in heap.
   static void IterateWeakRoots(ObjectVisitor* v);
 
+  // Iterates over weak roots that are bound to a given callback.
+  static void IterateWeakRoots(WeakReferenceGuest f,
+                               WeakReferenceCallback callback);
+
   // Find all weak handles satisfying the callback predicate, mark
   // them as pending.
   static void IdentifyWeakHandles(WeakSlotCallback f);