Reland r19897 "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 4eb178bc1b4c8758c651c335da8a3d3cca386491..f04a8bcb9a64105a496b8e4926cc833d06b7bc3a 100644
--- a/src/mark-compact.cc
+++ b/src/mark-compact.cc
@@ -1863,6 +1863,10 @@ 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;