Serializer enable/disable flags need thread safety.

src/ia32/assembler-ia32.cc

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // 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.
 //
@@ skipping 2686 matching lines @@
   EnsureSpace ensure_space(this);
   emit(data);
 }
 
 
 void Assembler::RecordRelocInfo(RelocInfo::Mode rmode, intptr_t data) {
   ASSERT(!RelocInfo::IsNone(rmode));
   // Don't record external references unless the heap will be serialized.
   if (rmode == RelocInfo::EXTERNAL_REFERENCE) {
 #ifdef DEBUG
-    if (!Serializer::enabled()) {
-      Serializer::TooLateToEnableNow();
-    }
+    Serializer::TrySetPermanentlyDisabled();
 #endif
     if (!Serializer::enabled() && !emit_debug_code()) {
       return;
     }
   }
   RelocInfo rinfo(pc_, rmode, data, NULL);
   reloc_info_writer.Write(&rinfo);
 }
 
 
@@ skipping 31 matching lines @@
     fprintf(coverage_log, "%s\n", file_line);
     fflush(coverage_log);
   }
 }
 
 #endif
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32