Changed scavenge GC to collect unmodified references

src/global-handles.cc

Index: src/global-handles.cc
diff --git a/src/global-handles.cc b/src/global-handles.cc
index 650999f394c5cc7c2e5397afff53c74e3c186d20..4c34744a50b04b49de4645416e73332c9ed48c43 100644
--- a/src/global-handles.cc
+++ b/src/global-handles.cc
@@ -687,6 +687,16 @@ void GlobalHandles::IterateNewSpaceWeakIndependentRoots(ObjectVisitor* v) {
 }
 
 
+void GlobalHandles::IdentifyWeakUnmodifiedObjects(WeakSlotCallback f) {
+  for (int i = 0; i < new_space_nodes_.length(); ++i) {
+    Node* node = new_space_nodes_[i];
+    if (node->IsWeak() && f(node->location())) {
+      node->set_partially_dependent(true);
+    }
+  }
+}
+
+
 bool GlobalHandles::IterateObjectGroups(ObjectVisitor* v,
                                         WeakSlotCallbackWithHeap can_skip) {
   ComputeObjectGroupsAndImplicitReferences();