Synchronize store buffer processing and concurrent sweeping.

src/store-buffer.h

Index: src/store-buffer.h
diff --git a/src/store-buffer.h b/src/store-buffer.h
index 01e7cbeb8d2a439784617f20a16a61793df14459..73b04e19e2a3d387eccd9572bd345a3b48fd4be7 100644
--- a/src/store-buffer.h
+++ b/src/store-buffer.h
@@ -41,7 +41,9 @@ class Page;
 class PagedSpace;
 class StoreBuffer;
 
-typedef void (*ObjectSlotCallback)(HeapObject** from, HeapObject* to);
+typedef void (*ObjectSlotCallback)(HeapObject** address,
+                                   HeapObject* new_value,
+                                   Object* old_value);
 
 typedef void (StoreBuffer::*RegionCallback)(Address start,
                                             Address end,