Serializer enable/disable flags need thread safety.

src/x64/assembler-x64.cc

 // 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 2935 matching lines @@
   emitl(data);
 }
 
 
 // Relocation information implementations.
 
 void Assembler::RecordRelocInfo(RelocInfo::Mode rmode, intptr_t data) {
   ASSERT(!RelocInfo::IsNone(rmode));
   if (rmode == RelocInfo::EXTERNAL_REFERENCE) {
     // Don't record external references unless the heap will be serialized.
-#ifdef DEBUG
-    if (!Serializer::enabled()) {
-      Serializer::TooLateToEnableNow();
-    }
-#endif
     if (!Serializer::enabled() && !emit_debug_code()) {
       return;
     }
   } else if (rmode == RelocInfo::CODE_AGE_SEQUENCE) {
     // Don't record psuedo relocation info for code age sequence mode.
     return;
   }
   RelocInfo rinfo(pc_, rmode, data, NULL);
   reloc_info_writer.Write(&rinfo);
 }
@@ skipping 50 matching lines @@
 
 
 bool RelocInfo::IsInConstantPool() {
   return false;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64