Use a per-isolate cache for the date object JS bits

src/runtime.h

 // 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 239 matching lines @@
   F(EnableAccessChecks, 1, 1) \
   F(SetAccessorProperty, 6, 1) \
   \
   /* Dates */ \
   F(DateCurrentTime, 0, 1) \
   F(DateParseString, 2, 1) \
   F(DateLocalTimezone, 1, 1) \
   F(DateToUTC, 1, 1) \
   F(DateMakeDay, 2, 1) \
   F(DateSetValue, 3, 1) \
+  F(DateCacheVersion, 0, 1) \
   \
   /* Numbers */ \
   \
   /* Globals */ \
   F(CompileString, 2, 1) \
   F(GlobalPrint, 1, 1) \
   \
   /* Eval */ \
   F(GlobalReceiver, 1, 1) \
   F(IsAttachedGlobal, 1, 1) \
@@ skipping 594 matching lines @@
 class AllocateDoubleAlignFlag:    public BitField<bool,            0, 1> {};
 class AllocateTargetSpace:        public BitField<AllocationSpace, 1, 3> {};
 
 class DeclareGlobalsEvalFlag:     public BitField<bool,         0, 1> {};
 class DeclareGlobalsNativeFlag:   public BitField<bool,         1, 1> {};
 class DeclareGlobalsLanguageMode: public BitField<LanguageMode, 2, 2> {};
 
 } }  // namespace v8::internal
 
 #endif  // V8_RUNTIME_H_