Don't clear map word when dominator and dominated HAllocate belong to the same basic block.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 7094cab29ea5acd180025e2b4148d524a9ba8c9c..6c821f21f918a194994a5e50d9cd648508607084 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -5543,7 +5543,7 @@ class HAllocate V8_FINAL : public HTemplateInstruction<2> {
             allocate->IsOldPointerSpaceAllocation());
   }
 
-  void ClearNextMapWord(int offset);
+  void ClearNextMapWord(HAllocate* dominated, int offset);
 
   Flags flags_;
   Handle<Map> known_initial_map_;