Snapshots: Add --extra-code flag to mksnapshot which lets you specify a file

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 428 matching lines @@
 DEFINE_string(testing_string_flag, "Hello, world!", "string-flag")
 DEFINE_int(testing_prng_seed, 42, "Seed used for threading test randomness")
 #ifdef WIN32
 DEFINE_string(testing_serialization_file, "C:\\Windows\\Temp\\serdes",
               "file in which to testing_serialize heap")
 #else
 DEFINE_string(testing_serialization_file, "/tmp/serdes",
               "file in which to serialize heap")
 #endif
 
+// mksnapshot.cc
+DEFINE_string(extra_code, NULL, "A filename with extra code to be included in"
+                  " the snapshot (mksnapshot only)")
+
 //
 // Dev shell flags
 //
 
 DEFINE_bool(help, false, "Print usage message, including flags, on console")
 DEFINE_bool(dump_counters, false, "Dump counters on exit")
 
 #ifdef ENABLE_DEBUGGER_SUPPORT
 DEFINE_bool(debugger, false, "Enable JavaScript debugger")
 DEFINE_bool(remote_debugger, false, "Connect JavaScript debugger to the "
@@ skipping 139 matching lines @@
             "Used with --prof, only does sampling and logging"
             " 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.")
 
+
 //
 // Disassembler only flags
 //
 #undef FLAG
 #ifdef ENABLE_DISASSEMBLER
 #define FLAG FLAG_FULL
 #else
 #define FLAG FLAG_READONLY
 #endif
 
@@ skipping 40 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