Reland r19897 "Fix memory leak caused by treating Code::next_code_link as strong in marker.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index edb7903cc24582fe4b631bb530a6bdaf232376eb..f931288c842a49a1c981189778106a0cf278f7ed 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1898,6 +1898,8 @@ class HeapObject: public Object {
   inline void IteratePointers(ObjectVisitor* v, int start, int end);
   // as above, for the single element at "offset"
   inline void IteratePointer(ObjectVisitor* v, int offset);
+  // as above, for the next code link of a code object.
+  inline void IterateNextCodeLink(ObjectVisitor* v, int offset);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(HeapObject);
@@ -5230,7 +5232,6 @@ class Code: public HeapObject {
   // the kind of the code object.
   //   FUNCTION           => type feedback information.
   //   STUB               => various things, e.g. a SMI
-  //   OPTIMIZED_FUNCTION => the next_code_link for optimized code list.
   DECL_ACCESSORS(raw_type_feedback_info, Object)
   inline Object* type_feedback_info();
   inline void set_type_feedback_info(
@@ -5563,8 +5564,8 @@ class Code: public HeapObject {
       kHandlerTableOffset + kPointerSize;
   static const int kTypeFeedbackInfoOffset =
       kDeoptimizationDataOffset + kPointerSize;
-  static const int kNextCodeLinkOffset = kTypeFeedbackInfoOffset;  // Shared.
-  static const int kGCMetadataOffset = kTypeFeedbackInfoOffset + kPointerSize;
+  static const int kNextCodeLinkOffset = kTypeFeedbackInfoOffset + kPointerSize;
+  static const int kGCMetadataOffset = kNextCodeLinkOffset + kPointerSize;
   static const int kICAgeOffset =
       kGCMetadataOffset + kPointerSize;
   static const int kFlagsOffset = kICAgeOffset + kIntSize;
@@ -10708,6 +10709,9 @@ class ObjectVisitor BASE_EMBEDDED {
   // Handy shorthand for visiting a single pointer.
   virtual void VisitPointer(Object** p) { VisitPointers(p, p + 1); }
 
+  // Visit weak next_code_link in Code object.
+  virtual void VisitNextCodeLink(Object** p) { VisitPointers(p, p + 1); }
+
   // To allow lazy clearing of inline caches the visitor has
   // a rich interface for iterating over Code objects..