Add initial semi-working producers profile.

src/global-handles.cc

Index: src/global-handles.cc
diff --git a/src/global-handles.cc b/src/global-handles.cc
index e51c4aadf13d68bd581064f33628caf8bbf588d6..f4b69fcdd3038b6c1ef322eac24612a1964cb7d3 100644
--- a/src/global-handles.cc
+++ b/src/global-handles.cc
@@ -264,6 +264,16 @@ void GlobalHandles::IterateWeakRoots(ObjectVisitor* v) {
 }
 
 
+void GlobalHandles::IterateWeakRoots(WeakReferenceGuest f,
+                                     WeakReferenceCallback callback) {
+  for (Node* current = head_; current != NULL; current = current->next()) {
+    if (current->IsWeak() && current->callback() == callback) {
+      f(current->object_, current->parameter());
+    }
+  }
+}
+
+
 void GlobalHandles::IdentifyWeakHandles(WeakSlotCallback f) {
   for (Node* current = head_; current != NULL; current = current->next()) {
     if (current->state_ == Node::WEAK) {