Add a check that weak object handle is not in NEAR_DEATH state after weak callback invocation.

include/v8.h

 // Copyright 2007-2009 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 119 matching lines @@
 
 }
 
 
 // --- W e a k  H a n d l e s
 
 
 /**
  * A weak reference callback function.
  *
+ * This callback should either explicitly invoke Dispose on |object| if
+ * V8 wrapper is not needed anymore, or 'revive' it by invocation of MakeWeak.
+ *
  * \param object the weak global object to be reclaimed by the garbage collector
  * \param parameter the value passed in when making the weak global object
  */
 typedef void (*WeakReferenceCallback)(Persistent<Value> object,
                                       void* parameter);
 
 
 // --- H a n d l e s ---
 
 #define TYPE_CHECK(T, S)                                       \
@@ skipping 3454 matching lines @@
 
 
 }  // namespace v8
 
 
 #undef V8EXPORT
 #undef TYPE_CHECK
 
 
 #endif  // V8_H_