Add map-based read barrier to WeakCell

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index d1e5acff893d65b008606969db7241a873602656..899a31ab3287667470836f978d2fadbdff8f56d2 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -2602,7 +2602,7 @@ class WeakFixedArray : public FixedArray {
 
   void Remove(Handle<HeapObject> value);
 
-  inline Object* Get(int index) const;
+  inline Object* Get(Heap* heap, int index) const;
   inline int Length() const;
 
   DECLARE_CAST(WeakFixedArray)
@@ -2616,6 +2616,7 @@ class WeakFixedArray : public FixedArray {
 
   static void Set(Handle<WeakFixedArray> array, int index,
                   Handle<HeapObject> value);
+  inline bool EqualAt(int index, Object* object) const;
   inline void clear(int index);
   inline bool IsEmptySlot(int index) const;
 
@@ -9762,7 +9763,8 @@ class PropertyCell: public Cell {
 
 class WeakCell : public HeapObject {
  public:
-  inline Object* value() const;
+  inline Object* value(Heap* heap);
+  inline Object* ValueNoReadBarrier();
 
   // This should not be called by anyone except GC.
   inline void clear();
@@ -9780,11 +9782,16 @@ class WeakCell : public HeapObject {
   DECLARE_VERIFIER(WeakCell)
 
   // Layout description.
-  static const int kValueOffset = HeapObject::kHeaderSize;
-  static const int kNextOffset = kValueOffset + kPointerSize;
+  static const int kValueOffsetDontForgetTheReadBarrier =
+      HeapObject::kHeaderSize;
+  static const int kNextOffset =
+      kValueOffsetDontForgetTheReadBarrier + kPointerSize;
   static const int kSize = kNextOffset + kPointerSize;
 
-  typedef FixedBodyDescriptor<kValueOffset, kSize, kSize> BodyDescriptor;
+  static inline void TriggerReadBarrier(Object* possible_weak_cell);
+
+  typedef FixedBodyDescriptor<kValueOffsetDontForgetTheReadBarrier, kSize,
+                              kSize> BodyDescriptor;
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(WeakCell);