[heap] Assert that there's no recodred slot corresponding to unboxed double field.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index d8140166de893781d70fbb7c1ee09dca61c49b1c..e36a99c281246201a83cb56cf103860421094f4b 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1172,6 +1172,8 @@ class Heap {
   void ClearRecordedSlot(HeapObject* object, Object** slot);
   void ClearRecordedSlotRange(Address start, Address end);
 
+  bool HasRecordedSlot(HeapObject* object, Object** slot);
+
   // ===========================================================================
   // Incremental marking API. ==================================================
   // ===========================================================================