[heap] Remove store buffer top from roots

src/heap/heap.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HEAP_HEAP_H_
 #define V8_HEAP_HEAP_H_
 
 #include <cmath>
 #include <map>
 
@@ skipping 15 matching lines @@
 
 using v8::MemoryPressureLevel;
 
 // Defines all the roots in Heap.
 #define STRONG_ROOT_LIST(V)                                                    \
   V(Map, byte_array_map, ByteArrayMap)                                         \
   V(Map, free_space_map, FreeSpaceMap)                                         \
   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)                                            \
   V(Oddball, true_value, TrueValue)                                            \
   V(Oddball, false_value, FalseValue)                                          \
   V(String, empty_string, empty_string)                                        \
   V(Oddball, uninitialized_value, UninitializedValue)                          \
   V(Map, cell_map, CellMap)                                                    \
   V(Map, global_property_cell_map, GlobalPropertyCellMap)                      \
   V(Map, shared_function_info_map, SharedFunctionInfoMap)                      \
@@ skipping 1026 matching lines @@
                                      Address end, bool record_slots,
                                      ObjectSlotCallback callback);
 
   // ===========================================================================
   // Store buffer API. =========================================================
   // ===========================================================================
 
   // 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);
 
   // ===========================================================================
   // Incremental marking API. ==================================================
   // ===========================================================================
 
   // Start incremental marking and ensure that idle time handler can perform
   // incremental steps.
@@ skipping 1559 matching lines @@
   friend class LargeObjectSpace;
   friend class NewSpace;
   friend class PagedSpace;
   DISALLOW_COPY_AND_ASSIGN(AllocationObserver);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_HEAP_H_