Use heap iterator in store buffer when page was swept precisely.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index e32b51d2ff06cff2fb9a5fbb9f0704fdf094fb58..9dda198e13abfb432e466a98c6251a25443760ab 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1747,6 +1747,10 @@ class HeapObject: public Object {
   // Returns the heap object's size in bytes
   inline int Size();
 
+  // Returns true if this heap object may contain pointers to objects in new
+  // space.
+  inline bool MayContainNewSpacePointers();
+
   // Given a heap object's map pointer, returns the heap size in bytes
   // Useful when the map pointer field is used for other purposes.
   // GC internal.