Cleaned up the weak lists hanging off the heap a bit.

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index ec8e941795b9dceb6f42df6802d50ec85c98f525..38013962dc4576e84e7b029c3d6b247f0004704d 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -2483,7 +2483,7 @@ void MarkCompactCollector::AfterMarking() {
 
 
 void MarkCompactCollector::ProcessMapCaches() {
-  Object* raw_context = heap()->native_contexts_list_;
+  Object* raw_context = heap()->native_contexts_list();
   while (raw_context != heap()->undefined_value()) {
     Context* context = reinterpret_cast<Context*>(raw_context);
     if (IsMarked(context)) {
@@ -3642,9 +3642,6 @@ void MarkCompactCollector::EvacuateNewSpaceAndCandidates() {
     }
   }
 
-  // Update the head of the native contexts list in the heap.
-  updating_visitor.VisitPointer(heap_->native_contexts_list_address());
-
   heap_->string_table()->Iterate(&updating_visitor);
   updating_visitor.VisitPointer(heap_->weak_object_to_code_table_address());
   if (heap_->weak_object_to_code_table()->IsHashTable()) {