Remove bogus forward declaration of ObjectGroup.

src/v8globals.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 144 matching lines @@
 class Smi;
 template <typename Config, class Allocator = FreeStoreAllocationPolicy>
     class SplayTree;
 class String;
 class Name;
 class Struct;
 class Variable;
 class RelocInfo;
 class Deserializer;
 class MessageLocation;
-class ObjectGroup;
 class VirtualMemory;
 class Mutex;
 
 typedef bool (*WeakSlotCallback)(Object** pointer);
 
 typedef bool (*WeakSlotCallbackWithHeap)(Heap* heap, Object** pointer);
 
 // -----------------------------------------------------------------------------
 // Miscellaneous
 
@@ skipping 393 matching lines @@
 
 enum ClearExceptionFlag {
   KEEP_EXCEPTION,
   CLEAR_EXCEPTION
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_V8GLOBALS_H_