Fix memory leak caused by treating Code::next_code_link as strong in marker.

src/mark-compact.cc

Index: src/mark-compact.cc
diff --git a/src/mark-compact.cc b/src/mark-compact.cc
index f5504478036709908462cd0832dd9fa369e5f570..d1335305152ada2f3c04500999e13663cb4297a6 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -1860,6 +1860,10 @@ class RootMarkingVisitor : public ObjectVisitor {
     for (Object** p = start; p < end; p++) MarkObjectByPointer(p);
   }
 
+  // Skip the weak next code link in a code object, which is visited in
+  // ProcessTopOptimizedFrame.
+  void VisitNextCodeLink(Object** p) { }
+
  private:
   void MarkObjectByPointer(Object** p) {
     if (!(*p)->IsHeapObject()) return;