Avoid sharing AccessorPairs during Genesis.

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index 32bf7a84b6f49124b29083654b75bb83884bae1e..2534dc74533963059f8231bba1e6450b4ab1f1b2 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -1219,6 +1219,10 @@ class Heap {
   // Verify the heap is in its normal state before or after a GC.
   void Verify();
 
+  // Verify that AccessorPairs are not shared, i.e. make sure that they have
+  // exactly one pointer to them.
+  void VerifyNoAccessorPairSharing();
+
   void OldPointerSpaceCheckStoreBuffer();
   void MapSpaceCheckStoreBuffer();
   void LargeObjectSpaceCheckStoreBuffer();