[heap] Prevent direct access to StoreBuffer.

src/assembler.cc

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 // - Redistributions of source code must retain the above copyright notice,
 // this list of conditions and the following disclaimer.
 //
@@ skipping 1123 matching lines @@
   return ExternalReference(isolate->regexp_stack()->limit_address());
 }
 
 
 ExternalReference ExternalReference::new_space_start(Isolate* isolate) {
   return ExternalReference(isolate->heap()->NewSpaceStart());
 }
 
 
 ExternalReference ExternalReference::store_buffer_top(Isolate* isolate) {
-  return ExternalReference(isolate->heap()->store_buffer()->TopAddress());
+  return ExternalReference(isolate->heap()->store_buffer_top_address());
 }
 
 
 ExternalReference ExternalReference::new_space_mask(Isolate* isolate) {
   return ExternalReference(reinterpret_cast<Address>(
       isolate->heap()->NewSpaceMask()));
 }
 
 
 ExternalReference ExternalReference::new_space_allocation_top_address(
@@ skipping 666 matching lines @@
 
 
 void Assembler::DataAlign(int m) {
   DCHECK(m >= 2 && base::bits::IsPowerOfTwo32(m));
   while ((pc_offset() & (m - 1)) != 0) {
     db(0);
   }
 }
 }  // namespace internal
 }  // namespace v8