Enable preemption in d8.

src/bootstrapper.h

 // 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 50 matching lines @@
   // Append code that needs fixup at the end of boot strapping.
   static void AddFixup(Code* code, MacroAssembler* masm);
 
   // Tells whether bootstrapping is active.
   static bool IsActive();
 
   // Encoding/decoding support for fixup flags.
   class FixupFlagsIsPCRelative: public BitField<bool, 0, 1> {};
   class FixupFlagsUseCodeObject: public BitField<bool, 1, 1> {};
   class FixupFlagsArgumentsCount: public BitField<uint32_t, 2, 32-2> {};
+  
+  // Support for thread preemption.
+  static int ArchiveSpacePerThread();
+  static char* ArchiveState(char* to);
+  static char* RestoreState(char* from);
 };
 
 }}  // namespace v8::internal
 
 #endif  // V8_BOOTSTRAPPER_H_