[heap] Remove store buffer top from roots

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index a5de6cc5958fcbabe9ed5cc5525e3f0c702414dd..7f70afaad21c54d034afe0d9caf25d79406a1e67 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -33,7 +33,6 @@ using v8::MemoryPressureLevel;
   V(Map, one_pointer_filler_map, OnePointerFillerMap)                          \
   V(Map, two_pointer_filler_map, TwoPointerFillerMap)                          \
   /* Cluster the most popular ones in a few cache lines here at the top.    */ \
-  V(Smi, store_buffer_top, StoreBufferTop)                                     \
   V(Oddball, undefined_value, UndefinedValue)                                  \
   V(Oddball, the_hole_value, TheHoleValue)                                     \
   V(Oddball, null_value, NullValue)                                            \
@@ -1080,9 +1079,7 @@ class Heap {
   // Write barrier support for object[offset] = o;
   inline void RecordWrite(Object* object, int offset, Object* o);
 
-  Address* store_buffer_top_address() {
-    return reinterpret_cast<Address*>(&roots_[kStoreBufferTopRootIndex]);
-  }
+  Address* store_buffer_top_address() { return store_buffer()->top_address(); }
 
   void ClearRecordedSlot(HeapObject* object, Object** slot);
   void ClearRecordedSlotRange(Address start, Address end);