Serializer enable/disable flags need thread safety.

src/mksnapshot.cc

 // Copyright 2006-2008 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 275 matching lines @@
   if (bz2_result != BZ_OK) {
     fprintf(stderr, "bzip error code: %d\n", bz2_result);
     exit(1);
   }
 #endif
   i::FLAG_logfile_per_isolate = false;
 
   Isolate* isolate = v8::Isolate::New();
   isolate->Enter();
   i::Isolate* internal_isolate = reinterpret_cast<i::Isolate*>(isolate);
-  i::Serializer::Enable(internal_isolate);
+  i::Serializer::RequestEnable(internal_isolate);
   Persistent<Context> context;
   {
     HandleScope handle_scope(isolate);
     context.Reset(isolate, Context::New(isolate));
   }
 
   if (context.IsEmpty()) {
     fprintf(stderr,
             "\nException thrown while compiling natives - see above.\n\n");
     exit(1);
@@ skipping 90 matching lines @@
       ser.CurrentAllocationAddress(i::OLD_DATA_SPACE),
       ser.CurrentAllocationAddress(i::CODE_SPACE),
       ser.CurrentAllocationAddress(i::MAP_SPACE),
       ser.CurrentAllocationAddress(i::CELL_SPACE),
       ser.CurrentAllocationAddress(i::PROPERTY_CELL_SPACE));
   isolate->Exit();
   isolate->Dispose();
   V8::Dispose();
   return 0;
 }