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

src/heap/heap.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HEAP_HEAP_H_
 #define V8_HEAP_HEAP_H_
 
 #include <cmath>
 
 #include "src/allocation.h"
@@ skipping 171 matching lines @@
     EmptySlowElementDictionary)                                                \
   V(Symbol, observed_symbol, ObservedSymbol)                                   \
   V(Symbol, uninitialized_symbol, UninitializedSymbol)                         \
   V(Symbol, megamorphic_symbol, MegamorphicSymbol)                             \
   V(Symbol, premonomorphic_symbol, PremonomorphicSymbol)                       \
   V(Symbol, generic_symbol, GenericSymbol)                                     \
   V(Symbol, stack_trace_symbol, StackTraceSymbol)                              \
   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)
 
 // Entries in this list are limited to Smis and are not visited during GC.
 #define SMI_ROOT_LIST(V)                                                   \
   V(Smi, stack_limit, StackLimit)                                          \
   V(Smi, real_stack_limit, RealStackLimit)                                 \
   V(Smi, last_script_id, LastScriptId)                                     \
   V(Smi, arguments_adaptor_deopt_pc_offset, ArgumentsAdaptorDeoptPCOffset) \
@@ skipping 2291 matching lines @@
   DisallowHeapAllocation no_allocation;  // i.e. no gc allowed.
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_HEAP_H_