Report promise reject with no handler (behind a flag).

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 87b939ad6c219986c192e33304fab1f76ff788d1..c304e7cde1972118d42dc760616d32c5c7577b06 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -189,6 +189,7 @@ namespace internal {
   V(Symbol, detailed_stack_trace_symbol, DetailedStackTraceSymbol)             \
   V(Symbol, normal_ic_symbol, NormalICSymbol)                                  \
   V(Symbol, home_object_symbol, HomeObjectSymbol)                              \
+  V(Symbol, promise_debug_symbol, PromiseDebugSymbol)                          \
   V(FixedArray, materialized_objects, MaterializedObjects)                     \
   V(FixedArray, allocation_sites_scratchpad, AllocationSitesScratchpad)        \
   V(FixedArray, microtask_queue, MicrotaskQueue)