Introduce --log-external-callbacks flag apart from --log-timer-events.

src/flag-definitions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 650 matching lines @@
             " when profiler is active (implies --noprof_auto).")
 DEFINE_bool(prof_browser_mode, true,
             "Used with --prof, turns on browser-compatible mode for profiling.")
 DEFINE_bool(log_regexp, false, "Log regular expression execution.")
 DEFINE_bool(sliding_state_window, false,
             "Update sliding state window counters.")
 DEFINE_string(logfile, "v8.log", "Specify the name of the log file.")
 DEFINE_bool(ll_prof, false, "Enable low-level linux profiler.")
 DEFINE_string(gc_fake_mmap, "/tmp/__v8_gc__",
               "Specify the name of the file for fake gc mmap used in ll_prof")
-DEFINE_bool(log_timer_events, false, "Log histogram timer events.")
+DEFINE_bool(log_timer_events, false, "Time events.")
+DEFINE_bool(log_external_callbacks, false, "Time external callbacks.")
+DEFINE_implication(log_external_callbacks, log_timer_events)
 
 //
 // Disassembler only flags
 //
 #undef FLAG
 #ifdef ENABLE_DISASSEMBLER
 #define FLAG FLAG_FULL
 #else
 #define FLAG FLAG_READONLY
 #endif
@@ skipping 41 matching lines @@
 #undef DEFINE_bool
 #undef DEFINE_int
 #undef DEFINE_string
 #undef DEFINE_implication
 
 #undef FLAG_MODE_DECLARE
 #undef FLAG_MODE_DEFINE
 #undef FLAG_MODE_DEFINE_DEFAULTS
 #undef FLAG_MODE_META
 #undef FLAG_MODE_DEFINE_IMPLICATIONS