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

src/global-handles.h

 // Copyright 2011 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 322 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(GlobalHandles);
 };
 
 
 class EternalHandles {
  public:
   enum SingletonHandle {
     I18N_TEMPLATE_ONE,
     I18N_TEMPLATE_TWO,
+    DATE_CACHE_VERSION,
 
     NUMBER_OF_SINGLETON_HANDLES
   };
 
   EternalHandles();
   ~EternalHandles();
 
   int NumberOfHandles() { return size_; }
 
   // Create an EternalHandle, overwriting the index.
@@ skipping 47 matching lines @@
   List<int> new_space_indices_;
   int singleton_handles_[NUMBER_OF_SINGLETON_HANDLES];
 
   DISALLOW_COPY_AND_ASSIGN(EternalHandles);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_GLOBAL_HANDLES_H_