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

src/flag-definitions.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.
 
 // This file defines all of the flags.  It is separated into different section,
 // for Debug, Release, Logging and Profiling, etc.  To add a new flag, find the
 // correct section, and use one of the DEFINE_ macros, without a trailing ';'.
 //
 // This include does not have a guard, because it is a template-style include,
 // which can be included multiple times in different modes.  It expects to have
@@ skipping 591 matching lines @@
            "in kBytes (default is 2 MB)")
 DEFINE_BOOL(log_regs_modified, true,
             "When logging register values, only print modified registers.")
 DEFINE_BOOL(log_colour, true, "When logging, try to use coloured output.")
 DEFINE_BOOL(ignore_asm_unimplemented_break, false,
             "Don't break for ASM_UNIMPLEMENTED_BREAK macros.")
 DEFINE_BOOL(trace_sim_messages, false,
             "Trace simulator debug messages. Implied by --trace-sim.")
 
 // isolate.cc
+DEFINE_BOOL(report_promise_reject, false,
+            "send messages for rejected promises with no reject handler")
 DEFINE_BOOL(stack_trace_on_illegal, false,
             "print stack trace when an illegal exception is thrown")
 DEFINE_BOOL(abort_on_uncaught_exception, false,
             "abort program (dump core) when an uncaught exception is thrown")
 DEFINE_BOOL(randomize_hashes, true,
             "randomize hashes to avoid predictable hash collisions "
             "(with snapshots this option cannot override the baked-in seed)")
 DEFINE_INT(hash_seed, 0,
            "Fixed seed to use to hash property keys (0 means random)"
            "(with snapshots this option cannot override the baked-in seed)")
@@ skipping 310 matching lines @@
 #undef DEFINE_ALIAS_FLOAT
 #undef DEFINE_ALIAS_ARGS
 
 #undef FLAG_MODE_DECLARE
 #undef FLAG_MODE_DEFINE
 #undef FLAG_MODE_DEFINE_DEFAULTS
 #undef FLAG_MODE_META
 #undef FLAG_MODE_DEFINE_IMPLICATIONS
 
 #undef COMMA