[serializer] make snapshot reproducible.

src/snapshot/mksnapshot.cc

 // Copyright 2006-2008 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.
 
 #include <errno.h>
 #include <signal.h>
 #include <stdio.h>
 
 #include "include/libplatform/libplatform.h"
 #include "src/assembler.h"
@@ skipping 121 matching lines @@
   }
   fclose(file);
   return chars;
 }
 
 
 int main(int argc, char** argv) {
   // By default, log code create information in the snapshot.
   i::FLAG_log_code = true;
   i::FLAG_logfile_per_isolate = false;
-
+  // Make mksnapshot runs predictable to create reproducible snapshots.
+  i::FLAG_predictable = true;
   // Print the usage if an error occurs when parsing the command line
   // flags or if the help flag is set.
   int result = i::FlagList::SetFlagsFromCommandLine(&argc, argv, true);
   if (result > 0 || (argc > 3) || i::FLAG_help) {
     ::printf("Usage: %s --startup_src=... --startup_blob=... [extras]\n",
              argv[0]);
     i::FlagList::PrintHelp();
     return !i::FLAG_help;
   }
 
@@ skipping 23 matching lines @@
     CHECK(blob.data);
     writer.WriteSnapshot(blob);
     delete[] blob.data;
   }
 
   V8::Dispose();
   V8::ShutdownPlatform();
   delete platform;
   return 0;
 }